JP2004032914A - System interconnection inverter and system interconnection system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system interconnection inverter for accurately correcting a DC component generated at output current, and to provide a system interconnection system. <P>SOLUTION: This system interconnection system includes an inverter 5 which is connected to a DC power supply 2, converts DC power into AC power and outputs it to a commercial system 3; a shunt 10 for detecting the output current of the inverter 5; a low-pass filter 11 for detecting the DC component from the output of the shunt 10; an isolated amplifier 13 for amplifying the output of the low-pass filter 11; a zero signal generator 14 for outputting the signal equivalent to the signal inputted into the isolated amplifier 13 to the isolated amplifier 13 at the predetermined timing when there is no output current of the inverter 5; a reference value storage circuit 16 for storing the output value of the isolated amplifier 13 when the signal from the zero signal generator 14 is inputted into the isolated amplifier 13 as a reference value; and an adder for correcting the reference value by the direct current component of the output current of the inverter 5 outputted from the isolated amplifier 13. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a system interconnection system using a solar cell, a fuel cell, and the like, and more particularly, to a technique for correcting a direct current component from being generated in an output current of a system interconnection inverter.
[0002]
[Prior art]
FIG. 7 shows a configuration example of a conventional system interconnection inverter disclosed in, for example, Japanese Patent Application Laid-Open No. 8-149842. In this figure, reference numeral 102 denotes a DC power source formed by a solar cell, a fuel cell, or the like; 108, a smoothing capacitor; 105, an internal switching element 105a for converting an input current to AC; Filter. Reference numeral 120 denotes a current detector, which is constituted by, for example, a Hall CT or a current transformer, and detects an output current of the inverter 105. The detection signal of the detected current is rectified by the full-wave rectifier circuit 127. Reference numeral 121 denotes a current command device that commands the current value of the output current of the inverter 105. The command signal of the current command device 121 is compared with the output signal of the full-wave rectifier circuit 127 by an adder 122, and the error is instantaneously controlled. The device 123 performs instantaneous waveform control by performing PWM control, PAM control, and the like on the switching element 105a of the inverter 105. After the instantaneous waveform control is performed, the output signal of the instantaneous waveform control device 123 is given to the switching element 105a of the inverter 105 by the gate drive circuit 124, and the output current controlled by the inverter 105 to a sine wave is obtained. An output terminal 109 is connected to a commercial system.
[0003]
Next, a circuit portion for correcting the DC component of the output current will be described. 110, a shunt for detecting the output current of the inverter 105; 111, a low-pass filter for detecting the DC component of the signal detected by the shunt 110; 113, an insulating amplifier for insulating and amplifying the output signal of the low-pass filter 111; Is an adder for adding the signal amplified by the insulation amplifier 113 to the detection signal of the current detector 120, and 125 is a DC component detection circuit, and when the signal amplified by the insulation amplifier 113 is higher than the built-in reference signal, Alternatively, when the signal is input for a predetermined time or more, or when one of the above reaches a predetermined value, a signal is output and input to the instantaneous waveform control device 123.
[0004]
In a system interconnection system composed of a DC power supply and an inverter, etc., when an instantaneous waveform control of the inverter or the output current is abnormal and a DC component is generated in the inverter output current, the inverter is connected to the output terminal. There is a problem that a DC component flows into a pole transformer of a commercial system or a transformer of another device connected to the commercial system, is DC-excited, and is damaged. The above-described prior art is a technique shown in view of this point. When a DC component is generated in the output current of the inverter 105, the DC component is detected, and the detection signal detected by the current detector 120 is subtracted by the adder 118. By performing the correction, an operation is performed to cancel the DC component of the output current.
[0005]
[Problems to be solved by the invention]
In the related art, when the level of the DC component of the output current of the inverter to be detected is extremely small, for example, when the DC component included in 100% of the output current of the inverter is 1%, the DC current is detected. Was very difficult. In addition, since the isolation amplifier is usually susceptible to changes in ambient temperature and voltage, the offset error of the isolation amplifier increases, and the DC component cannot be accurately detected. As a result, the DC component of the output current of the inverter is reduced. Was difficult to remove with high accuracy.
[0006]
In such a case, a high-precision insulation amplifier or a detection value when no DC component flows is stored as a reference level, and the detection value when the DC component is flowing is stored. Needs to be corrected. However, a method of making the isolation amplifier highly accurate is expensive and impractical. Further, in order to store the detected value when the DC component does not flow as the reference level, the inverter 8 may be temporarily stopped to disconnect the DC component, or the interconnection relay may be disconnected. As described in Japanese Patent Application Laid-Open No. 9-37568, for example, a detection value in a state where no DC component flows during a shipping test at a factory may be stored in advance as a reference level. However, there are the following problems. That is, when the inverter is temporarily stopped, for example, in the case of a solar power generation system, the solar cell is exposed to sunlight and can generate power, but the inverter is semi-forcibly stopped for one to several seconds. There is a problem that power cannot be generated, and even when the interconnection relay is disconnected, the output of the inverter is affected to some extent. Further, in the method described in Japanese Patent Application Laid-Open No. 9-37568, the reference level is limited to one, and when an amplifier that is easily affected by a change in ambient temperature or a change in voltage is used, the DC component cannot be accurately measured. There was a problem that it could not be detected well.
[0007]
By the way, according to the distributed power system interconnection guideline issued by the Institute for Electricity Safety and Environment in 1993, when the isolation transformer is not installed in the system interconnection type power converter, the DC component Is regulated to 1% or less of the rated output current of the power converter.
[0008]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object thereof is to provide a grid-connected inverter capable of accurately correcting a DC component generated in an output current, and a grid-connected inverter using the same. To provide a system.
[0009]
[Means for Solving the Problems]
A grid-connected inverter according to the present invention is connected to a DC power supply, converts DC power into AC power, and outputs the converted AC power to a commercial system, a shunt that detects an output current of the inverter, and an output of the shunt. A DC component detector for detecting a DC component, an amplifier for amplifying the output of the DC component detector, and a signal corresponding to a signal input to the amplifier when there is no output current of the inverter, at a predetermined timing. Zero adjustment means for outputting to the amplifier, reference value storage means for storing the output value of the amplifier when the signal from the zero adjustment means is input to the amplifier as a reference value, and the inverter output from the amplifier And an adder for subtracting and correcting the reference value stored in the reference value storage means from the DC component of the output current. In the following first, second and fourth embodiments, the zero adjustment command device, the zero signal generator and the input switch operate as zero adjustment means. In the third embodiment, the zero adjustment command device and the input short circuit Operate as zero adjustment means.
[0010]
Further, the system interconnection inverter according to the present invention is connected to a DC power supply, converts DC power to AC power and outputs the AC power to a commercial system, a shunt for detecting the output current of the inverter, and a shunt for the shunt. An amplifier for amplifying the output, a DC component detector for detecting a DC component from the output of the amplifier, and a signal corresponding to a signal input to the amplifier when there is no output current of the inverter, the voltage period of the commercial system. Zero adjustment means for outputting to the amplifier at a timing synchronized with the reference value; reference value storage means for storing, as a reference value, an output value of the amplifier when a signal from the zero adjustment means is input to the amplifier; and An adder for subtracting and correcting the reference value stored in the reference value storage means from the DC component of the output current of the inverter output from the component detector. A.
[0011]
An inverter connected to a DC power supply for converting DC power into AC power and outputting the AC power to a commercial system; a shunt detecting an output current of the inverter; an amplifier amplifying an output of the shunt; A DC component detector for detecting a DC component from an output, and a signal corresponding to a signal input to the amplifier when there is no output current of the inverter, which is output to the amplifier at a timing synchronized with a voltage cycle of the commercial system. Zero adjustment means, reference value storage means for storing the output value of the amplifier when the signal from the zero adjustment means is input to the amplifier as a reference value, and output current of the inverter output from the amplifier. An adder for subtracting and correcting the reference value stored in the reference value storage means.
[0012]
Further, as the zero adjusting means, a zero signal generator storing a signal corresponding to a signal input to the amplifier when there is no output current of the inverter is used.
[0013]
Further, a semiconductor element for short-circuiting between input terminals of the amplifier is used as the zero adjusting means.
[0014]
Further, the inverter is stopped when the reference value stored in the reference value storage means exceeds a predetermined value.
[0015]
Further, the output time of the zero adjusting means is set to less than 0.5 seconds.
[0016]
A DC component monitoring unit that detects a DC component corrected by the adder and outputs a signal for stopping the inverter when a DC component equal to or more than a predetermined value is detected for a predetermined time or more; When the output operation is performed, the DC component monitoring means does not perform the detection operation of the DC component, or does not output the inverter stop signal even if the DC component having the predetermined value or more is detected for the predetermined time or more. It is.
[0017]
A DC component monitoring means for detecting a DC component corrected by the adder and outputting a signal for stopping the inverter when a DC component of a predetermined value or more is detected for a predetermined time or more; When the means detects a DC component of a predetermined value or more, the zero adjusting means does not perform an output operation.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment according to the present invention will be described below with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 illustrates a system interconnection system according to a first embodiment of the present invention, and particularly illustrates a main configuration of a system interconnection inverter 1 that inputs power of a DC power supply and performs an interconnection operation with a commercial system. It is. The DC power supply includes a solar cell, a fuel cell, and the like. In this embodiment, the solar cell array 2 in which a plurality of solar cells are connected is used.
[0019]
As shown in FIG. 1, the output voltage of the solar cell array 2 is input to the DC-DC converter 4 of the grid-connected inverter 1. The DC-DC converter 4 converts an input voltage output from the solar cell array 2 into a voltage required for an input of the inverter 5 and outputs the voltage. The inverter 5 converts the DC power output from the DC-DC converter 4 into AC power and outputs the AC power. The inverter 5 removes high-frequency components by a waveform correction filter 7, and connects the AC power to the commercial system 3 via the interconnection relay 6. System.
[0020]
The output current of the inverter 5 is detected by the shunt 10, and a DC component is extracted by a low-pass filter 11 which is a DC component detector. The DC component output from the low-pass filter 11 is input to the insulation amplifier 13 via the input switch 12 when selected by the input switch 12. The insulation amplifier 13 insulates and amplifies the signal from the input switch 12.
[0021]
The zero signal generator 14 generates an output signal of the low-pass filter 11 when the output current of the inverter 5 is 0 A, that is, a signal corresponding to a signal input to the isolation amplifier 13 when there is no output current of the inverter 5. The value of the signal depends on what is used as the shunt 10. For example, when a shunt resistor is used as the shunt 10, 0 V is output. When a current sensor is used as the shunt 10, the output voltage when the input current of the current sensor is 0A is output. The output of the zero signal generator 14 is input to the insulation amplifier 13 via the input switch 12 when selected by the input switch 12.
[0022]
The input switch 12 is switched based on a command signal from the zero adjustment command unit 15. Here, the zero adjustment command device 15 outputs a command signal at an arbitrary timing and for an arbitrary time. For example, even when the inverter 5 is operating and a current is flowing through the shunt 10, a command signal can be output and the signal of the zero signal generator 14 can be output to the insulating amplifier 13. Here, if the arbitrary time for outputting the command signal of the zero adjustment command device 15 is set to less than 0.5 seconds, the detection time of the DC component of the output current of the inverter 5 by the DC component monitoring means 25 described later, that is, “ The influence on the detection of the detection time limit (within 0.5 seconds) specified in the "distributed power system interconnection guideline" can be reduced.
[0023]
The command signal from the zero adjustment command unit 15 is also input to a reference value storage circuit 16 which is a reference value storage means. The reference value storage circuit 16 is composed of a rewritable memory or the like, and updates and stores the output of the insulating amplifier 13 every time a command signal from the zero adjustment command unit 15 is input, and outputs the stored signal. Here, the output of the insulation amplifier 13 when the command signal from the zero adjustment command unit 15 is input is the output of the insulation amplifier 13 when the output current of the inverter 5 is 0 A, and the offset error of the insulation amplifier 13 Is equivalent to
[0024]
In the adder 17, the output of the reference value storage circuit 16 is subtracted from the output of the insulation amplifier 13. That is, the adder 17 outputs a DC component of the output current of the inverter 5 in which the offset error of the insulation amplifier 13 has been corrected. The output of the adder 17 is input to the adder 18.
[0025]
A current detector 20 including a current transformer (CT), a current transformer, and the like detects an AC component of an output current of the inverter 5 and outputs the detected AC component to the adder 18. In the adder 18, the AC component detected by the current detector 20 and the DC component output from the adder 17 are added and output as an inverter output current detection value.
[0026]
The current command device 21 commands the current value of the output current of the inverter 5. An error signal between the inverter output current detection value output from the adder 18 and the output of the current command device 21 is input to the instantaneous waveform controller 23 by the adder 22. The instantaneous waveform controller 23 controls the current value of the output current of the inverter 5 to a current commanded by the current command device 21. Thereby, the output current of the inverter 5 is controlled so that the instantaneous waveform is controlled and the DC component included in the output current of the inverter 5 is canceled. The gate drive circuit 24 controls the operation of the inverter 5 based on the output of the instantaneous waveform controller 23.
[0027]
The DC component of the output current of the inverter 5 is not canceled, and a current exceeding a predetermined current value (for example, when the rated output current of the grid-connected inverter is 16.5 A, 1% of 0.165 A) continues for a predetermined time. In this case, the DC component monitoring means 25 detects this, outputs a stop signal of the inverter 5 to the instantaneous waveform controller 23, and stops the inverter 5. Here, the “predetermined time” is preferably a value of less than 0.5 seconds based on the provisions of the “Distributed Power System Interconnection Guidelines”, for example, from 0.5 seconds to a zero adjustment time (for example, 0.02 seconds for 50 Hz) ) Is subtracted, and a value of less than 0.4 seconds is set in consideration of the margin.
[0028]
Here, when the zero adjustment commander 15 is outputting a command signal, the DC component monitoring means 25 does not perform the detection operation of the DC component, or even if the DC component of the predetermined value or more is detected for the predetermined time or more, the inverter is not operated. If the stop signal is not output, malfunction of the DC component monitoring means 25 can be prevented. Conversely, even if the zero adjustment commander 15 does not output a command signal when the DC component monitoring means 25 detects a DC component of a predetermined value or more, malfunction of the DC component monitoring means 25 is prevented. be able to.
[0029]
Further, when the output of the reference value storage circuit 16, that is, the offset error of the insulating amplifier 13 exceeds a predetermined current value (for example, 2 A), the abnormality detector 26 detects this, and the instantaneous waveform controller 23 stops the inverter 5. A signal is output, and the inverter 5 is stopped.
[0030]
As described above, in the present embodiment, the offset error of the insulating amplifier is corrected at an arbitrary timing and at an arbitrary time by the zero signal corresponding to the detection signal when the inverter output current is 0 A, so that it is easy and inexpensive. With this configuration, the DC component of the inverter output current can be accurately detected without being affected by the ambient temperature, the voltage, and the like. Further, the DC component of the inverter output current can be accurately corrected without stopping the inverter. Further, even if the DC component of the inverter output current increases for some reason, it can be detected and the inverter can be stopped. In the past, even if the offset error of the insulation amplifier became abnormally large, it could not be directly detected.However, the provision of the abnormality determiner allows the error to be eliminated even if the component such as the insulation amplifier becomes abnormal. Detect and stop the inverter.
[0031]
Further, in this embodiment, since the zero signal generator 14 is used, the offset error of the insulation amplifier 13 can be appropriately corrected according to the type of the shunt 10. In other words, the value of the signal input to the isolation amplifier 13 when there is no output current of the inverter 5 varies depending on the shunt used, but the value is appropriately stored by storing the value in the zero signal generator 14 in advance. be able to.
[0032]
Furthermore, by connecting a grid-connected inverter capable of accurately detecting the DC component of the inverter output current to a DC power source and using the output from the grid-connected inverter in a commercial system, A system interconnection system is obtained in which other devices connected to the commercial system are not likely to be damaged by the DC component.
[0033]
In the present embodiment, the low-pass filter 11, the zero signal generator 14, the zero adjustment command device 15, the reference value storage circuit 16, the abnormality detector 26, the DC component monitoring means 25, the current command device 21 Although the instantaneous waveform control 23, the adder 17, the adder 18, and the adder 22 are configured by hardware, all or any of them may be configured by software using a microcomputer or the like. For example, the insulation amplifier 13 includes an insulation amplification circuit (not shown) and an A / D converter (not shown), and includes a zero signal generator 14, a zero adjustment commander 15, a reference value storage circuit 16, The detector 26, the DC component monitoring means 25, the current command device 21, the instantaneous waveform control 23, the adder 17, the adder 18, and the adder 22 may be configured by software using a microcomputer. it can.
[0034]
Further, in the present embodiment, the insulating amplifier 13 is used, but the same effect can be obtained with a simple amplifier. Further, although the low-pass filter 11 is used as the DC component detector, a circuit that detects the DC component by calculating the average value of the current value for a certain period may be used.
[0035]
Embodiment 2 FIG.
In the first embodiment, the low-pass filter 11 for obtaining the DC component of the output current of the inverter 5 is provided on the output side of the shunt 10, but may be connected to the output side of the isolation amplifier 13. FIG. 2 shows a main part configuration of the system interconnection system in this case, particularly, a system interconnection inverter. The output current of the inverter 5 detected by the shunt 10 is input to the insulation amplifier 13 when selected by the input switch 12, and is insulated and amplified. When the input switch 12 is switched to the zero signal generator 14 by the zero adjustment command device 15, the output of the zero signal generator 14 is input to the isolation amplifier 13. The output of the insulation amplifier 13 is input to the low-pass filter 11, and a DC component is detected. The other configurations and operations are the same as those in the first embodiment, and a description thereof will not be repeated.
[0036]
When the low-pass filter 11 is connected to the output side of the insulating amplifier 13 as described above, a command signal is output from the zero adjustment command unit 15 at a timing synchronized with the voltage cycle of the commercial system 3, and the signal of the zero signal generator 14 is output. Must be output to the insulation amplifier 13. FIG. 3 shows the output waveform of each component in this case. FIG. 3A shows a voltage waveform of the commercial system 3. (B) is an output current waveform of the inverter 5, which has a DC component until timing t2.
[0037]
(C) is an output waveform of the zero adjustment command device 15, which outputs a command signal at a timing synchronized with the commercial system 3 and for an arbitrary time of less than 0.5 seconds. For example, once every 100 cycles of the commercial system 3, it turns on at the zero crossing point t 1, and the time of one voltage cycle of the commercial system 3, that is, 0.02 seconds when the commercial system 3 is 50 Hz, and 0.02 seconds when the commercial system 3 is 60 Hz It is set to turn off at time t2 when about 0.016 seconds have elapsed.
[0038]
(D) is an input signal of the isolation amplifier 13, and the inverter 5 detected by the shunt 10 until t1 when there is no command signal from the zero adjustment command unit 15 and the input switch 12 selects the shunt 10; Output current is input. During the period from t1 to t2 when the command signal is output from the zero adjustment command device 15, the output of the zero signal generator 14 is input.
[0039]
(E) is an output signal of the insulating amplifier 13, and an output between t1 and t2 is an offset error of the insulating amplifier 13. (F) is an output signal of the reference value storage circuit 16. (G) is an output signal of the low-pass filter 11, which is a signal corresponding to a DC component of the inverter 5.
[0040]
From the timing t2, it can be seen that the DC component in which the offset error of the insulating amplifier 13 has been corrected is output from the low-pass filter 11. Note that, although simplified in the figure, the output of the low-pass filter 11 actually changes gradually near the timing t2. Then, it can be seen that the output current (b) of the inverter 5 has a waveform from which the DC component has been removed after the timing t2.
[0041]
Next, the output of each component when the output of the zero adjustment command device 15 is not synchronized with the commercial system 3 in the circuit configuration shown in FIG. 2 will be described with reference to FIG. In FIG. 4, (a) to (g) show output waveforms of the same parts as in FIG. As shown in (c), the output of the zero adjustment commander 15 is not synchronized with the commercial system 3 and is output when the inverter output during one cycle of the commercial system 3 is +. When the command signal is output from the zero adjustment command device 15, the input of the insulating amplifier 13 is zero, and an offset error appears on the output side. The reference value storage circuit 16 stores the offset error, and outputs the stored offset error signal as shown in FIG.
[0042]
However, in the low-pass filter 11, the output waveform of the insulating amplifier 13 is averaged to extract a DC component. Therefore, the signal of the waveform partially missing on the + side is averaged by the command of the zero adjustment command unit 15, thereby obtaining the negative side. The erroneous DC component shifted to the above is output. For this reason, the DC component included in the output current of the inverter 5 cannot be accurately removed, and a current in which the DC component remains after the timing t2 is output as shown in (b).
[0043]
As described above, according to the second embodiment, the low-pass filter 11 is connected to the output side of the insulating amplifier 13 to detect the DC component from the output of the insulating amplifier 13, and is synchronized with the voltage cycle of the commercial system 3. Since the signal of the zero signal generator 14 is output to the isolation amplifier 13 at the timing described above, the DC component of the inverter output current can be accurately corrected without stopping the inverter as in the first embodiment. And a timer or the like for determining the signal generation timing can be omitted.
[0044]
Furthermore, by connecting a grid-connected inverter capable of accurately detecting the DC component of the inverter output current to a DC power source and using the output from the grid-connected inverter in a commercial system, A system interconnection system is obtained in which other devices connected to the commercial system are not likely to be damaged by the DC component.
[0045]
In the case of the circuit configuration in the first embodiment, the output of the low-pass filter 11 does not become abnormal even if the output of the zero adjustment command device 15 is not synchronized with the voltage cycle of the commercial system 3. By synchronizing the output of the zero adjustment commander 15 with the voltage cycle of the commercial system 3, an effect is obtained that a timer or the like for determining the signal generation timing can be omitted.
[0046]
Embodiment 3 FIG.
FIG. 5 shows a grid interconnection system according to a third embodiment of the present invention, and particularly illustrates a main configuration of a grid interconnection inverter. The difference from the first embodiment shown in FIG. 1 is that the zero signal generator and the input switch are eliminated, and an input short circuit 30 is provided instead. This embodiment is effective when a shunt resistor or the like that outputs 0 V when there is no output current from the inverter 5 is used as the shunt 10. Hereinafter, a specific description will be given. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
[0047]
The output current of the inverter 5 is detected by the shunt 10, and the DC component is detected by the low-pass filter 11. The DC component output from the low-pass filter 11 is input to the input short circuit 30.
[0048]
The input short circuit 30 is a circuit for short-circuiting the input terminals of the insulation amplifier 13 and is configured using a semiconductor element such as a photocoupler, for example, and operates based on a command signal from the zero adjustment command device 15. When the input short circuit 30 operates, the input terminals of the isolation amplifier 13 are forcibly short-circuited regardless of the output of the low-pass filter 11. When the input terminals of the insulating amplifier 13 are short-circuited, a signal corresponding to a signal input to the insulating amplifier 13 when there is no output current of the inverter 5 is input to the insulating amplifier 13. In order to prevent a short-circuit current from the output of the shunt 10 and the low-pass filter 11, the input short-circuit 30 includes a unit (not shown) for suppressing a short-circuit current due to a resistor or the like.
[0049]
On the other hand, when the command signal from the zero adjustment command device 15 is not output and the input short circuit 30 is not operating, the output of the low-pass filter 11 is input to the isolation amplifier 13 as it is. The insulation amplifier 13 insulates and amplifies the input signal.
[0050]
The zero adjustment command device 15 outputs a command signal at an arbitrary timing and for an arbitrary time. For example, even when the inverter 5 is operating and a current is flowing through the shunt 10, a command signal is output and the input short-circuit 30 can short-circuit the input terminals of the insulating amplifier 13. Here, similarly to the above embodiments, if the arbitrary time for outputting the command signal of the zero adjustment command device 15 is set to less than 0.5 seconds, the DC current The influence on the detection time of the component, that is, the detection time limit (within 0.5 seconds) specified in the "Distributed Power System Interconnection Guidelines" can be reduced.
[0051]
Also, as in the second embodiment, the time of one voltage cycle of the commercial system 3, that is, the time of the commercial system 3, that is, once every 100 cycles of the commercial system 3, The command signal may be output for 0.02 seconds when the frequency of the system 3 is 50 Hz and for about 0.016 seconds when the frequency of the system 3 is 60 Hz. As described above, if the command signal of the zero adjustment command device 15 is output in synchronization with the commercial system 3, the output of the low-pass filter 11 becomes abnormal even when the low-pass filter 11 is connected to the output side of the insulating amplifier 13. It will not be. Further, a timer or the like for determining the signal generation timing can be omitted.
[0052]
The command signal from the zero adjustment command unit 15 is also input to the reference value storage circuit 16. The reference value storage circuit 16 is composed of a rewritable memory or the like, and updates and stores the output of the insulating amplifier 13 every time a command signal from the zero adjustment command unit 15 is input, and outputs the stored signal. Here, the output of the insulation amplifier 13 when the command signal from the zero adjustment command device 15 is input is the output of the insulation amplifier 13 when the input of the insulation amplifier 13 is short-circuited. This corresponds to an offset error. Other operations are the same as those of the system interconnection inverter in the first embodiment.
[0053]
As described above, according to the third embodiment, the offset terminals of the insulating amplifier 13 are corrected by short-circuiting the input terminals of the insulating amplifier 13 at a predetermined timing and time. As in the embodiment, the DC component of the inverter output current can be accurately detected with an easy and inexpensive configuration without stopping the inverter or disconnecting the interconnection relay. In addition, since the zero adjustment commander and the input short circuit are used as the zero adjustment means, the circuit configuration is simpler and less expensive than in each of the above embodiments using a zero signal generator and an input switch.
[0054]
A latching relay can be used as the input short circuit 30. However, if a semiconductor device such as a photocoupler is used as described above, since the reaction time is fast, zero adjustment can be performed frequently, and the timing of adjustment can be reduced. Can be performed finely with respect to the cycle of the commercial system 3, and it is easy to match the zero-cross point of the voltage of the commercial system 3. Therefore, even if the offset error of the insulating amplifier 13 changes due to ambient temperature, voltage, or the like, it can be corrected with high accuracy, and the detection accuracy of the DC component of the inverter output current can be further increased.
[0055]
Further, similarly to the first embodiment, even if the DC component of the inverter output current increases for some reason, it can be detected and the inverter can be stopped. In the past, even if the offset error of the insulation amplifier became abnormally large, it could not be directly detected.However, the provision of the abnormality determiner allows the error to be eliminated even if the component such as the insulation amplifier becomes abnormal. Detect and stop the inverter.
[0056]
Furthermore, by connecting a grid-connected inverter capable of accurately detecting the DC component of the inverter output current to a DC power source and using the output from the grid-connected inverter in a commercial system, A system interconnection system is obtained in which other devices connected to the commercial system are not likely to be damaged by the DC component.
[0057]
In FIG. 5, the low-pass filter 11 is placed on the output side of the shunt 10, but the same effect can be obtained by connecting it to the output side of the insulating amplifier 13. In this case, the output of the low-pass filter 11 is output to the reference value storage circuit 16 and the adder 17.
[0058]
Embodiment 4 FIG.
In each of the above embodiments, the current detector 20 is used for feedback of the instantaneous waveform control. However, the insulating amplifier 13 may be used as a feedback amplifier. FIG. 6 shows a main part configuration diagram of the system interconnection system in this case, particularly the system interconnection inverter. As shown in the figure, according to this embodiment, the current detector 20 and the adder 18 provided in each of the above embodiments become unnecessary. Hereinafter, a specific description will be given.
[0059]
As shown in the figure, the grid-connected inverter according to the present embodiment includes a shunt 10 that detects an output current of the inverter 5, an insulating amplifier 13 that insulates and amplifies the output of the shunt 10, A low-pass filter 11 that detects a DC component from an output, a zero adjustment commander 15 that outputs a command signal at a predetermined timing, and a signal corresponding to a signal input to the isolation amplifier 13 when there is no output from the inverter 5 is stored. Based on the output of the zero signal generator 14 and the output of the zero adjustment command unit 15, whether the output from the shunt 10 is input to the isolation amplifier 13 or the output from the zero signal generator 14 is input to the isolation amplifier 13 And a reference value for storing an output from the low-pass filter 11 when a signal from the zero signal generator 14 is input to the isolation amplifier 13 And a 憶回 path 16. Then, the output of the insulating amplifier 13 and the output of the reference value storage circuit 16 are input to the adder 19, and the offset error of the insulating amplifier 13 is corrected from the output current of the inverter 5. This is different from the above embodiments in which the offset error of the insulating amplifier 13 is corrected from the DC component of the output current of the inverter 5.
[0060]
The corrected output current of the inverter 5 is input to the adder 22, and an error from the output of the current command device 21 is input to the instantaneous waveform control unit 23. The instantaneous waveform controller 23 controls the current value of the output current of the inverter 5 to be the current value commanded by the current command device 21.
[0061]
The DC component of the output current of the inverter 5 output from the low-pass filter 11 is input to the DC component monitoring means 25, and when a DC component of a predetermined value or more occurs for a predetermined time or more, the instantaneous waveform A stop signal for inverter 5 is output to controller 23, and inverter 5 is stopped.
[0062]
As described above, according to this embodiment, the offset error of the amplifier can be corrected with a simpler configuration without using the current detector, and the DC component of the inverter output current can be corrected with high accuracy. it can.
[0063]
Also, by connecting a grid-connected inverter capable of accurately detecting the DC component of the inverter output current to a DC power supply and using the output from the grid-connected inverter in a commercial system, It is possible to obtain a system interconnection system in which other devices connected to the commercial system are not likely to be damaged by a DC component.
[0064]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the grid connection inverter which concerns on this invention, the DC component of an inverter output current can be corrected accurately by correct | amending the error of an amplifier at predetermined timing, without stopping an inverter.
[0065]
Further, according to the grid interconnection system of the present invention, it is possible to obtain a grid interconnection system in which a commercial system and other devices connected to the commercial system are not likely to be damaged by a DC component.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a main part of a system interconnection inverter according to a first embodiment.
FIG. 2 is a main part configuration diagram of a system interconnection inverter in a second embodiment.
FIG. 3 is a diagram showing output waveforms of respective components of a system interconnection inverter according to a second embodiment.
FIG. 4 is a diagram showing output waveforms of respective components of a system interconnection inverter according to a second embodiment.
FIG. 5 is a main part configuration diagram of a system interconnection inverter in a third embodiment.
FIG. 6 is a main part configuration diagram of a system interconnection inverter according to a fourth embodiment.
FIG. 7 is a main part configuration diagram of a conventional system interconnection inverter.
[Explanation of symbols]
1 grid-connected inverter, 2 solar array, 3 commercial grid, 5 inverter, 10 shunt, 11 low-pass filter, 12 input switch, 13 isolation amplifier, 14 zero signal generator, 15 zero adjustment commander, 16 reference value Memory circuit, 17 adder, 19 adder, 25 DC component monitoring means, 26 abnormality detector, 30 input short circuit.

Claims (10)

An inverter that is connected to a DC power supply, converts DC power into AC power, and outputs the AC power to a commercial grid;
A shunt detecting the output current of the inverter;
A DC component detector for detecting a DC component from the output of the shunt;
An amplifier for amplifying the output of the DC component detector;
Zero adjustment means for outputting a signal corresponding to a signal input to the amplifier at a predetermined timing to the amplifier when there is no output current of the inverter;
Reference value storage means for storing, as a reference value, the output value of the amplifier when the signal from the zero adjustment means is input to the amplifier;
A grid-connected inverter comprising: an adder for subtracting and correcting the reference value stored in the reference value storage means from the DC component of the output current of the inverter output from the amplifier. An inverter that is connected to a DC power supply, converts DC power into AC power, and outputs the AC power to a commercial grid;
A shunt detecting the output current of the inverter;
An amplifier for amplifying the output of the shunt;
A DC component detector for detecting a DC component from the output of the amplifier,
Zero adjustment means for outputting a signal corresponding to a signal input to the amplifier when there is no output current of the inverter to the amplifier at a timing synchronized with a voltage cycle of the commercial system,
Reference value storage means for storing, as a reference value, the output value of the amplifier when the signal from the zero adjustment means is input to the amplifier;
A system interconnection inverter comprising: an adder for subtracting and correcting the reference value stored in the reference value storage means from the DC component of the output current of the inverter output from the DC component detector. An inverter that is connected to a DC power supply, converts DC power into AC power, and outputs the AC power to a commercial grid;
A shunt detecting the output current of the inverter;
An amplifier for amplifying the output of the shunt;
A DC component detector for detecting a DC component from the output of the amplifier,
Zero adjustment means for outputting a signal corresponding to a signal input to the amplifier when there is no output current of the inverter to the amplifier at a timing synchronized with a voltage cycle of the commercial system,
Reference value storage means for storing, as a reference value, the output value of the amplifier when the signal from the zero adjustment means is input to the amplifier;
A system interconnected inverter comprising: an adder for subtracting and correcting the reference value stored in the reference value storage means from the output current of the inverter output from the amplifier. The said zero adjustment means has the zero signal generator which stored the signal corresponding to the signal input into the said amplifier when there is no output current of the said inverter, The said Claim 1 thru | or 3 characterized by the above-mentioned. The system interconnection inverter according to any one of the above. 4. The system interconnection inverter according to claim 1, wherein the zero adjustment unit includes a semiconductor element that short-circuits between input terminals of the amplifier. 5. The grid-connected inverter according to any one of claims 1 to 5, wherein the inverter is stopped when a reference value stored in the reference value storage means is equal to or more than a predetermined value. 7. The system interconnection inverter according to claim 1, wherein an output time of said zero adjusting means is less than 0.5 seconds. DC component monitoring means for detecting a DC component corrected by the adder, and outputting a signal for stopping the inverter when a DC component of a predetermined value or more is detected for a predetermined time or more, wherein the zero adjustment means outputs During the operation, the DC component monitoring means does not perform the detection operation of the DC component, or does not output the inverter stop signal even if the DC component of the predetermined value or more is detected for the predetermined time or more. The grid-connected inverter according to any one of claims 1 to 7, characterized in that: DC component monitoring means for detecting a DC component corrected by the adder and outputting a signal for stopping the inverter when a DC component of a predetermined value or more is detected for a predetermined time or more, The system interconnection according to any one of claims 1 to 7, wherein the zero adjustment unit does not perform an output operation when a DC component equal to or more than a predetermined value is detected. Inverter. 10. A system interconnection system comprising: the system interconnection inverter according to claim 1; and a DC power supply that outputs DC power to the system interconnection inverter.

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