JP4172235B2 - Grid-connected inverter device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a grid-connected inverter device that converts DC power, such as a solar cell or a fuel cell, into AC power having a commercial frequency and injects power into the system.
[0002]
[Prior art]
In this type of conventional grid-connected inverter, first power conversion means for boosting a DC input voltage and second power conversion means for performing step-down and inverter operation are connected in series, and a capacitor of several tens of μF or less is connected to the connection portion. In order to increase the efficiency in addition to the sine wave of the output current waveform by switching the high frequency operation of the first power conversion means and the second power conversion means when generating the output current waveform, Miniaturization is realized (see, for example, Patent Document 1).
[0003]
FIG. 8 is a connection diagram showing a configuration of a grid-connected inverter device that is conventionally used. Here, the DC power source 1 is constituted by a distributed power source having a DC output such as a solar cell or a fuel cell. The grid interconnection inverter supplies AC power to the grid 5 at a commercial frequency of 50/60 Hz with a DC power supply as an input. The grid interconnection inverter includes a first power conversion means 2 that boosts the input voltage to a voltage higher than the grid voltage, an intermediate stage capacitor 3 of several tens of μF or less that removes high frequency components of the boosted voltage, and a waveform shaping of the output current into a sine wave. The second power conversion means 4 is connected to the grid 5. In particular, the first power conversion means 2 is composed of a capacitor 2a for smoothing the input voltage, a DC reactor 2b for storing boosted energy, a switching element 2c, and a diode 2d, and the second power conversion means 4 is a full circuit using four switching elements. It comprises a bridge inverter 4a, an AC reactor 4b, and a filter capacitor 4c.
[0004]
The operation will be described below. Since the intermediate-stage capacitor 3 voltage must be at least several tens of volts higher than the system voltage in order to inject power into the system 5, for example, when the input voltage is DC 200V and the system voltage is AC 200V, the voltage of the intermediate stage capacitor 3 is 4 The voltage is boosted for ˜5 ms to control the output current, and boosting is not performed in a period where the absolute value of the other system voltage is sufficiently smaller than the input voltage. As a result, the high-frequency switching operation of the first power conversion means 2 is performed only partially within one cycle of the system, so that the loss of the switching element 2c is remarkably reduced, and the input / output of the second power conversion means 4 is further reduced. Since the potential difference is kept low, the switching loss of the full bridge inverter 4a constituting the second power conversion means can also be reduced. Accordingly, the shape of the heat sink for cooling is reduced, and the capacity of the intermediate capacitor 3 is also reduced, so that the overall shape can be reduced, and it is possible to realize an inexpensive device with improved efficiency and reduced size and weight. .
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-152661 [0006]
[Problems to be solved by the invention]
However, in the above-described conventional configuration, since the direct current reactor in the first power conversion means and the alternating current reactor in the second power conversion means share the output current control, respectively, a plurality of reactors and current detection means are necessary. In addition to the limitations in device efficiency, cost reduction, size reduction, and weight reduction, it is difficult to improve reliability because the control circuit becomes complicated. In addition, since the two power conversion means are connected in series, when controlling one reactor current, the current passing through the other reactor may resonate with a nearby filter capacitor, and noise It had the problem of becoming a source.
[0007]
The present invention is a system capable of realizing low loss, small size and light weight by generating one reactor for a plurality of power conversion means and one control means when generating a sine wave current from a DC power supply. The object is to provide a connected inverter device.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides first power conversion means for stepping down a DC input voltage, second power conversion means for performing a step-up operation connected in series to the output of the first power conversion means, The third power conversion means connected in series to the output of the two power conversion means and performing a commercial switching operation, and the first power conversion means and the second power conversion means have one reactor, 3 by the output of the power converter controls the current of the reactor so that the sine wave current, a third power conversion means having a polarity switching function, high efficiency and to be injected into the system and generates an alternating current waveform An inexpensive and lightweight grid-connected inverter device is provided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, the first power conversion unit that steps down the DC input voltage and the second power conversion unit that is connected in series to the output and performs the step-up operation are current-controlled by one reactor, so that the large size It is a grid-connected inverter device that can be reduced in price, reduced in size and weight, and simplified in control.
[0010]
According to a second aspect of the present invention, in the configuration in which only one of the first power conversion means and the second power conversion means performs waveform control by high frequency operation, the high frequency operation is switched depending on the magnitude of the system voltage and the DC input voltage. Thus, a grid-connected inverter device that realizes a high-efficiency and low-distortion sinusoidal current is obtained.
[0011]
According to the third aspect of the present invention, the operation switching timing of the first power conversion means and the second power conversion means determined by the magnitude relationship between the system voltage and the DC input voltage can be corrected with respect to the system voltage phase. Therefore, it is a grid-connected inverter device that realizes a higher quality sine wave current.
[0012]
In the invention described in claim 4, by disposing a capacitor of several tens of μF or less between the second power conversion unit and the third power conversion unit arranged in series, the distortion of the output current waveform is not deteriorated. The grid-connected inverter device is capable of reducing the high-frequency noise level.
[0013]
In the invention described in claim 5, the first power conversion means and the second power conversion means for individually converting the power to the plurality of DC input power sources are arranged, and the current is output on the output side of the second power conversion means. By synthesizing, a simple grid-connected inverter device that does not require a plurality of grid protection means is obtained.
[0014]
【Example】
(Example 1)
A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment. The grid-connected inverter device of this embodiment injects electric current from a DC power source 11 which is a distributed power source such as a solar cell or a fuel cell, into the system 17 as a synchronous sine wave. The output of the first power conversion means 13 constituted by the first switching element 13a and the first diode 13b and the input of the second power conversion means 14 constituted by the second switching element 14a and the second diode 14b are a reactor. 15 are connected in series. Further, the output of the second power conversion means 14 is converted into alternating current by the third power conversion means 16 constituted by the polarity switching inverter 16a and the filter capacitor 16b, and is connected to the grid.
[0015]
The operation of the grid-connected inverter device configured as described above will be described. Here, the first power conversion means 13 instantaneously controls the amplitude of the current waveform of the reactor 15 by stepping down the input voltage and modulating the on-time by the high-frequency chopping operation of the first switching element 13a. The second power conversion means 14 instantaneously controls the amplitude of the current waveform of the reactor 15 by boosting the input voltage and modulating the on-time by the high-frequency chopping operation of the second switching element 14a. For example, when the system voltage is 200 V AC, the voltage changes from 0 V to about 280 V. Therefore, as long as the input voltage is within this range, the step-down operation and the step-up operation are required within one commercial cycle. When the first power conversion means 13 performs the step-down wave operation, the second switching element 14a in the second power conversion means 14 is always off, and when the second power conversion means 14 performs the step-up wave operation, The first switching element 14a in the power conversion means 14 is always on. On the other hand, the polarity switching inverter 16a having a full bridge configuration that constitutes the third power conversion means 16 performs switching at the commercial frequency in synchronization with the positive / negative of the system voltage, and the commercial double obtained from the output of the second power conversion means 14 The frequency current is converted into a sinusoidal alternating current synchronized with the system 17.
[0016]
As described above, according to the present embodiment, the first power conversion means for performing the step-down operation and the second power conversion means for performing the step-up operation are exclusively operated, and the current of the reactor disposed only is controlled. Because it is possible to reduce the number of large-sized reactors that have been required in the past, it is possible to realize an inexpensive, small, lightweight, low-loss grid-connected inverter device, including simplified control circuits. it can.
[0017]
(Example 2)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing the configuration of this embodiment. 2 differs from the circuit configuration of FIG. 1 in that an input voltage detecting means 18 for detecting a DC input voltage and a system voltage detecting means 19 for detecting a system voltage are arranged, and each detected value is compared in the control circuit 20. This is the point that the drive signal is sent to the first switching element 13a and the second switching element 14a after being performed. Components other than those described above are the same as those in the first embodiment, and a description thereof will be omitted.
[0018]
About the grid connection inverter apparatus comprised as mentioned above, operation | movement is demonstrated with reference to the wave form diagram of FIG. Information obtained by the input voltage detection means 18 and the system voltage detection means 19 is compared inside the control circuit 20, and when the input voltage is larger than the system voltage, the control circuit 20 inputs to the first power conversion means 13. The step-down operation is performed by sending a drive signal for high-frequency chopping of the voltage, and the amplitude of the current waveform of the reactor 15 is instantaneously controlled by modulating the on-time. At this time, the second switching element 14 a in the second power conversion means 14 is always off, and the current passing through the reactor current becomes the output current of the second power conversion means 14. When the input voltage is smaller than the system voltage, the control circuit 20 always turns on the first switching element 13a to make the input voltage of the reactor 15 coincide with the voltage of the DC power supply 11, and to the second power conversion means 14. By applying a drive signal for high-frequency switching operation to the second switching element 14a, the input voltage of the DC power supply 11 is boosted and the on-time is modulated to instantaneously control the amplitude of the current waveform of the reactor 15. The current obtained at the output of the second power conversion means 14 in this way is converted into a sine wave alternating current synchronized with the system 17 by the polarity switching inverter 16 a having a full bridge configuration constituting the third power conversion means 16.
[0019]
As described above, according to the present embodiment, by comparing the input voltage of the DC power supply and the system voltage and sharing the step-down operation and the step-up operation within the commercial cycle, the input voltage change is particularly large as in the distributed power supply. Since the switching timing between the step-down operation and the step-up operation can be detected with high accuracy even in a DC power supply, a grid-connected inverter device capable of obtaining a sinusoidal alternating current with less distortion can be realized.
[0020]
(Example 3)
Hereinafter, a third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram showing the configuration of this embodiment. 4 differs from the circuit configuration of FIG. 2 in that the phase correction means 21 for correcting the timing obtained inside the control circuit 20 by the input voltage detection means 18 and the system voltage detection means 19 is different from the first switching element and the first switching element. It is the point arrange | positioned in the input stage of the drive signal to 2 switching elements. Components other than those described above are the same as those in the second embodiment, and a description thereof will be omitted.
[0021]
The operation of the grid-connected inverter device configured as described above will be described with reference to the waveform diagram of FIG. Usually, the switching phase between the high frequency operation of the first power conversion means 13 and the high frequency operation of the second power conversion means 14 is obtained by comparing the magnitudes of the input voltage and the absolute value of the system voltage. However, although the input voltage of the first power conversion means 13 is made constant by the smoothing capacitor 12, the current injected into the system operates at a power factor of 1, so that it is constant particularly when the current injected into the system is large. Ripple is generated. In such a case, when the high frequency operation of the first power conversion means 13 and the second power conversion means 14 is switched at the timing obtained from the detected values of the input voltage and the system voltage, the current injected into the system 17 in the vicinity of the switching phase. May cause waveform distortion. Here, the phase correction means 21 gives an arbitrary advance or delay phase to the drive signals output from the control circuit 20 to the first switching element 13a and the second switching element 14a, so that the current injected into the system 17 is Waveform shaping to sine wave with less high frequency.
[0022]
As described above, according to this embodiment, the high-frequency operation switching phase of the first power conversion means and the second power conversion means is advanced or delayed with respect to the timing obtained from the comparison between the input voltage and the system voltage. By correcting, it is possible to provide a grid-connected inverter device that can realize the injection of a high-quality waveform with few harmonic components into the grid.
[0023]
Example 4
The fourth embodiment of the present invention will be described below with reference to FIG. FIG. 6 is a block diagram showing the configuration of this embodiment. 6 is different from the circuit configuration of FIG. 1 in that a high frequency filter capacitor 22 is arranged between the second power conversion unit 14 and the third power conversion unit 16. Components other than those described above are the same as those in the first embodiment, and a description thereof will be omitted.
[0024]
The operation of the grid-connected inverter device configured as described above will be described. The current generated by the high frequency operation of the first power conversion unit 13 and the second power conversion unit 14 is a high frequency component which is an operating frequency of the first switching element 13a and the second switching element 14a in addition to a commercial double frequency low frequency component. Is a superimposed waveform. The high frequency current component contained in the output current of the second power conversion means 14 is removed by the high frequency filter capacitor 22 arranged at the input of the polarity switching inverter 16a, and the current passing through the polarity switching inverter 16a is a low frequency component of the commercial frequency. Therefore, the loss in the polarity switching inverter 16a due to the high-frequency current is reduced, and the high-frequency wiring is also shortened, so that generated noise is reduced.
[0025]
As described above, according to the present embodiment, by arranging the high frequency filter capacitor at the output stage of the second power conversion means, only the current from which the high frequency component has been removed passes through the polarity switching inverter. Therefore, it is possible to provide a grid-connected inverter device capable of realizing high-efficiency operation.
[0026]
(Example 5)
Hereinafter, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a block diagram showing the configuration of this embodiment. 7 is different from the circuit configuration of FIG. 1 in that the input power supply is a plurality of first DC power supply 11a and second DC power supply 11b, and the first power conversion means 13 and the second power conversion means 14 are arranged respectively. In the above, the outputs of the plurality of second power conversion means 13 are combined and connected at the input stage of the third power conversion means, and the system protection device 23 is disposed between the third power conversion means and the system. . Components other than those described above are the same as those in the first embodiment, and a description thereof will be omitted.
[0027]
The operation of the grid-connected inverter device configured as described above will be described. From the DC power sources 11a and 11b having different input voltages, a commercial double frequency current synchronized with the system 17 is generated by the reactor 15 connected between the first power converter 13 and the second power converter 14, respectively. Generated. Synchronous modulation currents obtained from the outputs of the plurality of second power conversion means 14 are combined at the input stage of the polarity switching inverter 16a, and the third power conversion means 16 outputs a sine wave current. A system protection device 23 is disposed between the system 17 and the third power conversion means 16, and performs an operation of disconnecting the system interconnection inverter from the system 17 when the frequency or voltage of the system 17 is abnormal.
[0028]
As described above, according to the present embodiment, even when there are a plurality of distributed power sources having different voltages, current waveforms modulated individually by the first power conversion unit and the second power conversion unit are generated and synthesized. By injecting current into the system with the polarity switching inverter, the system protection device for disconnecting the inverter from the system can be unified, so that an inexpensive system interconnection inverter device can be realized.
[0029]
【The invention's effect】
As described above, the invention according to any one of claims 1 to 5 aims at sharing the reactor by arranging the second power conversion means for performing the boosting operation in series with the output of the first power conversion means for performing the step-down operation, Since the two conversion means share the waveform control within the commercial cycle, it is possible to reduce the large reactor for current control, which has been necessary in the past, so it is inexpensive, including simplification of the control circuit, small size, light weight, A low-loss system interconnection inverter device can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a grid interconnection inverter apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a grid interconnection inverter apparatus according to a second embodiment of the present invention. FIG. 3 is a waveform diagram showing the operation of each part of the grid-connected inverter device according to the second embodiment of the present invention. FIG. 4 is a block diagram showing the configuration of the grid-connected inverter device according to the third embodiment of the present invention. FIG. 5 is a waveform diagram showing the operation of each part of the grid-connected inverter device according to the third embodiment of the present invention. FIG. 6 shows the configuration of the grid-connected inverter device according to the fourth embodiment of the present invention. FIG. 7 is a block diagram showing the configuration of a grid-connected inverter device according to a fifth embodiment of the present invention. FIG. 8 is a block diagram showing the configuration of a conventional grid-connected inverter device.
11 DC power supply 11a 1st DC power supply (plural DC input power supplies)
11b Second DC power supply (plural DC input power supplies)
12 smoothing capacitor 13 first power conversion means 13a first switching element 13b first diode 14 second power conversion means 14a second switching element 14b second diode 15 reactor 16 third power conversion means 16a polarity switching inverter 16b filter capacitor 17 system 18 Input voltage detection means 19 System voltage detection means 20 Control circuit 21 Phase correction means 22 High frequency filter capacitor 23 System protection device

Claims (5)

A first power converting means for stepping down a DC input voltage; a second power converting means connected in series to the output of the first power converting means to perform a step-up operation; and connected in series to the output of the second power converting means. And a third power converter that performs a commercial switching operation. The first power converter and the second power converter have one reactor, and the output of the third power converter is a sine wave current. The grid connection inverter apparatus which controls the electric current of the said reactor so that it may become .   In a configuration having system voltage detection means for detecting system voltage and DC input voltage detection means for detecting DC input voltage, and only one of the first power conversion means and the second power conversion means performs high-frequency operation. The grid-connected inverter device according to claim 1, wherein the high-frequency operation is switched according to the magnitude of the voltage and the DC input voltage.   3. The grid interconnection inverter according to claim 2, wherein the operation switching timing of the first power conversion means and the second power conversion means can be corrected with respect to the grid voltage phase.   4. The grid-connected inverter device according to claim 1, wherein a capacitor of several tens of μF or less is arranged between the second power conversion means and the third power conversion means arranged in series.   The plurality of DC input power supplies are connected to first power conversion means and second power conversion means for performing power conversion individually for each DC input power supply, and the output of the second power conversion is the power by the third power conversion means. The grid connection inverter apparatus of any one of Claim 1 to 4 synthesize | combined.

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