JPH01107661A - System-connected inverter device - Google Patents

Abstract

PURPOSE:To effectively use power, by controlling the voltage at both ends of an electrolytic capacitor to be made equal to reference voltage higher than the peak voltage of a commercial power. CONSTITUTION:The output direct current of a solar battery 1 is fed to an electrolytic capacitor 3 via a diode 2, and is fed to an inverter 4 with ripple removed. By the inverter 4, direct current is converted to alternating current, and is connected to a commercial power system 7 via an AC switch 5 in a closed state, and is fed to a load 6. Then, voltage at both ends of the electrolytic capacitor 3 is detected by a DC voltage detector 8, and detection voltage due to the detector 8 and reference voltage higher than the peak voltage of the system 7 due to a reference power source 11 are compared with each other by a controlling means 16, and the output of the inverter 4 is controlled by the controlling means 16. As a result, even if the inverter 4 is set in a stopped state, current is not to flow to the capacitor 3 from the system 7.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention converts the output DC of a DC power source such as a solar battery into AC using an inverter, and connects it to a commercial power grid to supply the converted AC to a load. The present invention relates to a grid-connected inverter device.

[Conventional technology]

Conventionally, a grid-connected inverter device converts the output DC of a DC power source such as a solar battery into AC using an inverter, connects it to the commercial power grid, and supplies the converted AC to the load.
For example, there is a solar power generation system as shown in FIG.

Figure 2 shows the basic configuration of a solar power generation system, in which (1) is a solar cell as a DC power source, and (2) is a backflow prevention device whose anode is connected to the positive output terminal of solar cell (1). (3) has a diode (2) on both ends.
An electrolytic capacitor (4) is connected to the cathode of the solar cell (1) and the negative terminal of the solar cell (1), an inverter (4) converts the output direct current of the solar cell (1) into alternating current, a switching element such as a transistor, and the switching element. The input terminals of the diodes connected in parallel in opposite directions are connected to both ends of the capacitor (3).

(5) is an AC switch whose one end is connected to one output terminal of the inverter (4), and (6) is an AC switch whose both ends are connected to the other end of the switch (5) and the other output terminal of the inverter (4). The load (7) is a commercial power system, which is connected to both ends of the load (6), and is connected to the commercial power system (7) so that the output AC of the inverter (4) is transmitted to the load via the switch (5). (6).

By the way, in the case of such a system, in order to parallel the system to system (7) and disassociate it from system (7),
By closing and opening the AC switch (5), the system (
7) has the problem of adverse effects such as noise caused by instantaneous voltage fluctuations and switching surges.

Moreover, the system paralleling and disconnection described above are carried out in the morning and evening when the system is started or stopped, or when there is an abnormality in the system or the system (7), especially in the morning.

In the evening or on cloudy days, the amount of solar radiation is unstable, so the current or voltage of the solar cell (1) or the amount of solar radiation fluctuates around the threshold for stably driving the inverter (4).
The switch (5) repeatedly opens and closes, causing the system to be connected to and disconnected from the system frequently, and the instantaneous voltage fluctuations and noise described above frequently occur in the system (7). become.

Therefore, conventionally, in order to eliminate such inconvenience, for example, Japanese Patent Application Laid-Open No. 59-76122 (HO2J 11
As described in 00), hysteresis is provided in the thresholds such as the current and voltage of the solar cell (1) and the amount of solar radiation per unit in order to stably drive the inverter (4), or from the disassembly to the parallel connection of the system. It is being considered to set a long delay time to reduce the number of repetitions of dequeueing and rejoining.

[Problem that the invention seeks to solve]

However, as mentioned above, hysteresis is provided for the output of the solar cell (1) when driving the inverter (4) and the threshold value of the amount of solar radiation. Even if set up, it will be discontinued.

Although the number of repetitions of parallel entries can be reduced to some extent, it is not possible to completely eliminate the negative effect on the system (7), and neither can be considered a fundamental solution. There is a problem in that the power generated by the solar cell (1) within the solar cell cannot be effectively utilized.

Therefore, the technical object of the present invention is to significantly reduce the number of grid connections and disconnections, and to effectively utilize the power of a DC power source such as a solar battery.

[Failure to solve the problem]

Means for solving the problems of the prior art described above will be explained using FIG. 1 corresponding to an embodiment.

That is, in this invention, a solar cell (
1) and a transistor (4a) as a switching element
) ~(4d) and each transistor (4a) ~(
The transistor (4a) is composed of diodes (4e) to (4h) connected in parallel in opposite directions to the transistor (4d), respectively.
) to (4d), the solar cell (1)
An inverter (
4), an electrolytic capacitor (3) provided in parallel with the solar cell (1), a DC voltage detector (8) that detects the voltage across the capacitor (3), and the detector (8).
a control means αQ for comparing the detected voltage with a reference voltage higher than the peak voltage of the commercial power system (7) and controlling the output of the inverter so that the detected voltage becomes equal to the reference voltage; The inverter stop command circuit αη detects a decrease in the output of (1) below the set value and outputs a stop command to the inverter (4).

[For production]

Therefore, according to the present invention, the output DC of the solar cell (1) is transmitted through the electrolytic capacitor (3) via the diode (2).
), the lip is removed by the electrolytic capacitor (3), and the capacitor is supplied to the inverter (4).
4) converts the output DC of the solar cell (1) into AC, and connects it to the commercial power system (7) via the closed AC switch (5).
), and the alternating current converted by the inverter (4) is supplied to the load (6).

By the way, the voltage across the electrolytic capacitor (3) is detected by the DC voltage detector (8), and the voltage detected by the detector (8) and the reference voltage higher than the peak voltage of the commercial power system (7) by the reference power supply Qυ are determined. are compared by the control means αφ, and the output of the inverter (4) is controlled by the control means α· so that the detected voltage becomes equal to the reference voltage.

At this time, the voltage on the input side of the inverter (4) is maintained at a constant value higher than the peak voltage of the commercial power grid (7), so when the output of the solar cell (1) drops below the set value, the inverter Even if the inverter (4) is stopped by the stop command from the stop command circuit Q7), the inverter (4)
) is higher than the output voltage, so no current from the system (7) flows to the capacitor (3) via the diodes (4e) to (4h) of the inverter (4) Even if the output of the solar cell (1) fluctuates, there is no need to disconnect the output of the inverter (4) from the grid (7) using an AC switch, etc. You only need to do this when there is an abnormality in (7) or the inverter device.
Compared to the conventional system, the number of times of grid paralleling and disconnection is greatly reduced, preventing the adverse effects on the grid (7) such as instantaneous voltage fluctuations and surge noise. Compared to the case where a delay time is provided, the number of grid connections can be reduced, the number of disconnections can be reduced, and electric power can be used more effectively.

〔Example〕

Next, the present invention will be explained in detail with reference to FIG. 1 showing an embodiment thereof.

In the figure, (4a) and (4b) are electrolytic capacitors (
(4C) and (4d) are two NPN transistors as switching elements connected in series to both ends of the electrolytic capacitor (3). type transistor, (4
e), (4f), (4g), and (4h) are flywheel diodes connected in parallel to each transistor (4a) to (4d) in opposite directions, and (4i) and (4j) are connected in series. Connect the reactor μ for the filter and the filter capacitor, one end of the reactor/L/(41) is connected to the emitter of the transistor (4a), and the other end of the capacitor (4j) is connected to the emitter of the transistor (4C). It is.

Each transistor (4a) to (4d), each diode (
4e) to (4h), reactor/L/ (4i), and capacitor (4j) constitute an inverter (4), and the capacitor (4) serves as both output terminals of the inverter (4).
4j) is connected to one end of the switch (5) and the other end of the load (6).

(8) is a DC voltage detector that detects the DC voltage across the electrolytic capacitor (3), (9) is an AC voltage detector that detects the load voltage supplied to the load (6), and 00 is the inverter (4). an AC current detector consisting of a current transformer or the like installed in the current-carrying path between the AC switch (5) and the AC switch (5); αη is a reference power source that provides a reference voltage higher than the peak voltage of the commercial power system (7); 2) is a constant DC voltage control circuit, which compares the voltage detected by the DC voltage detector (8) with the reference voltage,
A positive deviation signal is output only when the former detection voltage is higher than the latter reference voltage.

(to) is a multiplier that multiplies the output of the DC voltage constant control circuit (2) and the output of the AC voltage detector (9), and α→ is the input of the output of multiplier a3 and the output of AC current detector αQ. αG is an inverter control circuit, and the output of the error amplifier αG is input as a current command value, and the switching control signal based on the input current command value is sent to the inverter (4). ) for each transistor (
4a) to (4d), one set of transistors (4a), (4d) and another set of transistors (
4b) and (4C) are alternately switched to control the output of the inverter (4). AC voltage detector (9), reference power supply αυ, DC/DC voltage establishment control circuit) 1 Multiplier At this time, the error amplifier α and the inverter control circuit constitute a control means αe.

αη is an inverter stop command circuit, which derives the power generated by the solar cell (1) based on the amount of solar radiation, and detects when the output voltage of the solar cell (1) has fallen below a set value near the optimum operating point. Then, a stop command signal is output to the inverter control circuit (to) to stop the output of the switching control signal from the inverter control circuit aθ.

Note that the 'AC switch (5) is a different type from the conventional one.
It is opened only when there is an abnormality such as a failure or an accident in the data storage device or the commercial power system (7), and is kept closed at all other times.

Then, the output DC of the solar cell (1) is supplied to the electrolytic capacitor (3) via the backflow prevention diode (2), the ripple is removed by the electrolytic capacitor (3), and the output DC is supplied to the inverter (4). The output direct current of the solar cell (1) is converted into alternating current by the inverter (4), which is connected to the commercial power grid (7) via the closed AC switch (5) and converted by the inverter (4). Alternating current is supplied to the load (6).

By the way, the voltage across the electrolytic capacitor (3) is detected by the DC voltage detector (8), and the voltage detected by the detector (8) and the reference voltage from the reference power supply αυ are compared by the DC voltage constant control circuit (2). , only when the former detection voltage is higher than the latter reference voltage, a positive deviation signal is output from the control circuit (6) and input to the multiplier α [present].

Furthermore, the multiplier (to) multiplies the output of the control circuit @ and the output of the AC voltage detector (9), and the error amplifier a→
As a result, the error between the output of the multiplier (to) and the output of the AC current detector α0 is amplified, and the inverter control circuit QFJ sets the inverter (4) as the current command value using the amplified error.
) output control is performed.

Therefore, the voltage across the electrolytic capacitor (3) is held constant equal to the reference voltage, which is higher than the peak voltage of the commercial power system (7), and the load voltage of the load (6), that is, the voltage of the commercial power system (7). A current having the same phase as the voltage is supplied to the load (6) by the inverter (4), and the power generated by the solar cell (1) can be efficiently supplied to the load (6) with a power factor of l.

When the amount of solar radiation is sufficient and the power generated by the solar cell (1) is sufficiently large, AC power corresponding to the output of the solar cell (1) is supplied from the inverter (4) to the load (6).

On the other hand, when the amount of solar radiation is insufficient and the power generated by the solar cell (1) is small, such as in the morning, evening, or on cloudy days, the output voltage of the solar cell (1) decreases and the backflow prevention diode (
2) enters the reverse bias state, and the operation of the inverter stop command circuit αη stops the output of the switching control signal from the inverter control circuit αG to the inverter (4), thereby stopping the operation of the inverter (4).

At this time, since the voltage on the input side of the inverter (4) is maintained at a constant value equal to the reference voltage higher than the peak voltage of the commercial power system (7), the inverter (4) ) is stopped, the voltage on the input side of the inverter (4) is higher than the voltage on the output side, so the diode (4e
) to (4h), the current from the grid (7) does not flow to the capacitor (3), and even if there is a fluctuation in the output of the solar cell (1), the output of the inverter (4) is controlled by an AC switch, etc. It is no longer necessary to disconnect the system and the system (7), and the system parallelization and disconnection only need to be performed when there is an abnormality in the system (7) or the inverter device. The number of times will be significantly reduced.

Therefore, according to the embodiment, the electrolytic capacitor (3
) by setting the voltage at a constant value higher than the peak voltage of the commercial power grid (7) and keeping the voltage at the input side of the inverter (4) constant, the power generated by the solar cell (1) decreases. Even if the inverter (4) is stopped due to the operation of the inverter stop command circuit αη, the voltage on the input side of the inverter (4) is higher than the voltage on the output side, so the diodes (4e) to Current from the grid (7) does not flow to the capacitor (3) through the capacitor (4h), and even if there is a fluctuation in the output of the solar cell (1), the output of the inverter (4) is controlled by the AC switch (5). It is no longer necessary to disconnect the system (7) and the system (7), and it is only necessary to connect and disconnect the system only when there is an abnormality in the system (7) or the inverter device.
Compared to the conventional system, the number of parallel connections and disconnections can be significantly reduced, and the system (such as instantaneous voltage fluctuations and surge noise)
7), and moreover, the number of grid connections and disconnections can be reduced, and the effective use of power can be achieved, compared to the conventional case where several people are connected to the grid and hysteresis or delay time is provided when disconnecting the grid. It becomes possible to achieve this goal.

Note that the DC power source is not limited to the solar cell (1) described above.

Furthermore, it goes without saying that the control means αQ is not limited to the configuration described above.

〔Effect of the invention〕

As described above, according to the grid-connected inverter device of the present invention, the voltage across the electrolytic capacitor is controlled to be equal to the reference voltage higher than the peak voltage of the commercial power grid, so it is independent of the output fluctuation of the DC power supply. , the voltage on the input side of the inverter can be maintained at a higher voltage than the output side, and even if the inverter is stopped, current from the grid can be prevented from flowing to the electrolytic capacitor via the inverter's diode. This eliminates the need to repeatedly connect and disconnect from the grid using an AC switch in response to fluctuations in the output of the DC power supply, and it is possible to connect and disconnect from the grid only when there is an abnormality in the system or inverter device. It is often possible to prevent negative effects on the grid such as instantaneous voltage fluctuations and surge noise due to repeated paralleling and uncoupling of the grid, and moreover, it is possible to prevent hysteresis and delay time when paralleling and uncoupling the grid as in the past. The number of parallel connections and disconnections from the grid can be further reduced, and power can be used more effectively.

[Brief explanation of the drawing]

1A is a block diagram of one embodiment of the grid-connected inverter device of the present invention, and FIG. 2 is a connection diagram of a conventional example. (1)... Solar cell, (3)... Electrolytic capacitor,
(4)...Inverter, (6)...Load, (7)...
... Commercial power system, (8) ... DC voltage detector, αυ
...Reference power source, αe...Control means, αη...Inverter stop command circuit.

Claims (1)

[Claims] (1) Consisting of a DC power supply, a switching element, and a diode connected in parallel in the opposite direction to the switching element, the output DC of the DC power supply is converted into AC by switching of the switching element, and the converted AC is used as commercial power. an inverter connected to a power grid and supplied to a load; an electrolytic capacitor installed in parallel with the DC power supply; a DC voltage detector that detects the voltage across the capacitor; and a voltage detected by the detector and the commercial power supply. control means for controlling the output of the inverter so that the detected voltage is equal to the reference voltage by comparing the detected voltage with a reference voltage higher than the peak voltage of the electric power system; A grid-connected inverter device comprising: an inverter stop command circuit that detects and outputs a stop command to the inverter.