JP4100125B2 - Grid-connected inverter device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power conversion 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 a system.
[0002]
[Prior art]
FIG. 12 is a connection diagram illustrating 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 direct-current power generated by the direct-current power source 1 is converted into high-frequency power by the first inverter 2 and is then stepped up and down by the high-frequency transformer 3 to be transmitted to the secondary side. The high frequency power generated on the secondary side of the high frequency transformer is converted into a unidirectional pulsating flow by the rectifying means 4 and then converted into commercial AC power synchronized with the system 6 by the second inverter 5 and injected into the system It is. Here, each of the first inverter and the second inverter is connected in a full bridge by four switching elements.
[0003]
The operation will be described below. In this embodiment, the switching elements Qa to Qd of the first inverter 2 are repeatedly turned on and off, whereby the DC voltage is chopped and a positive and negative rectangular voltage is applied to the primary side of the high-frequency transformer 3. By performing pulse width modulation that changes the conduction ratio of each switching element within the commercial cycle, the average value of the secondary voltage of the high-frequency transformer is a sine wave. The current of the current limiting reactor 5 generated by the difference between the voltage generated on the secondary side and the system voltage is removed of the high frequency component by the filter capacitor 6, and the input current of the second inverter 7 becomes a commercial double frequency pulsating current. ing. The second inverter 7 is synchronized with the polarity of the system 8 and Q1 and Q4 and Q2 and Q3 are repeatedly turned on and off, whereby the second inverter input current is converted into alternating current and current is injected into the system 8.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-169567 [0005]
[Problems to be solved by the invention]
However, in the conventional configuration, in the process of converting the high frequency power into the commercial frequency power, the high frequency power is once rectified and then reconverted into an alternating current having a different frequency, so that a plurality of power converters are required. Accordingly, there is a problem in that loss occurs in each conversion stage, resulting in poor efficiency, and further, a cooling space for heat radiation becomes large and the shape of the device becomes large.
[0006]
An object of the present invention is to provide a grid-connected inverter that can realize low loss, small size, and light weight by making AC-AC conversion from high-frequency power to commercial frequency power simple. .
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the grid-connected inverter device of the present invention uses a bidirectional semiconductor switch for an inverter that converts high-frequency power into commercial frequency power, and can eliminate the conventionally required high-frequency power rectifying means, A low-loss, small, lightweight, and inexpensive grid-connected inverter.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The invention described in claim 1 includes: a high-frequency transformer; a first inverter disposed on a primary side of the high-frequency transformer that converts DC power into high-frequency power; and the high-frequency transformer that converts the high-frequency power into commercial power. A current-limiting reactor disposed on the secondary side, and a second inverter having a plurality of switching elements configured as a full bridge, wherein the switching element of the second inverter is configured by a bidirectional switch, The bidirectional switch is turned on / off according to the polarity of the system voltage to provide a grid-connected inverter device that converts the power of the high-frequency transformer into alternating current, thereby realizing conversion from the rectifier and direct current to alternating current with a single inverter. It is a grid-connected inverter device.
[0009]
The invention described in claim 2 has regenerative power processing means in which an electrolytic capacitor and a bidirectional switch are connected in series, and the regenerative power processing means is arranged in parallel with a high-frequency transformer and a second inverter, and 2. The grid-connected inverter device according to claim 1, wherein the bidirectional switch in the regenerative power processing means is turned on only when a low power factor load is connected during independent operation of the inverter. It is a grid-connected inverter device that can realize power regeneration.
[0010]
【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 the present embodiment includes a DC power source 11 that is a distributed power source such as a solar cell or a fuel cell, an inverter 12 that converts DC power into high-frequency power, a high-frequency transformer that converts high-frequency power voltage, The current limiting reactor and the second inverter 15 in which the bidirectional switch 16 is configured as a full bridge are configured, and the output of the second inverter is connected to the system to inject a synchronous sine wave current.
[0011]
The operation of the grid-connected inverter device configured as described above will be described with reference to the waveform diagram of FIG. Due to the difference between the rectangular wave-shaped high-frequency voltage generated on the secondary side of the high-frequency transformer and the system voltage, a current in a delayed phase flows through the current-limiting reactor 14.
[0012]
On the other hand, the bidirectional switch 16 of the second inverter 15 is turned on / off according to the polarity of the system voltage. For example, when the system voltage is positive, the current-limiting reactor current is positive in the direction shown in the figure. The current limiting reactor current passes through Q1 and Q4. Here, since the current is blocked by Q2 and Q3 during the negative period, the current passing through the second inverter 15 becomes a high-frequency pulsating flow as illustrated. The high-frequency component of the current-limiting reactor current is removed by the AC filter capacitor 17, and a commercial frequency component synchronized with the system 18 is injected into the system 18 as an output current.
[0013]
As described above, according to the present embodiment, by using an inverter configured with a bidirectional switch, high-frequency power can be directly converted into commercial-frequency power, so that a plurality of conversion stages are not required. It is possible to realize a low-loss, small and light system interconnection inverter device.
[0014]
(Example 2)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram showing the configuration of this embodiment. 3 is different from the circuit configuration of FIG. 1 in that an AC reactor 20 is arranged at the output of the second inverter 15 instead of the current-limiting reactor located on the secondary side of the high-frequency transformer. Components other than those described above are the same as those in the first embodiment, and a description thereof will be omitted.
[0015]
The operation of the grid-connected inverter device configured as described above will be described with reference to the waveform diagram of FIG. Due to the difference between the rectangular wave-shaped high-frequency voltage generated on the secondary side of the high-frequency transformer and the system voltage, a current having a delayed phase flows through the AC reactor 20. Here, the second inverter 15 performs high-frequency switching. Specifically, when the AC reactor current is positive with respect to the illustrated direction, Q1 and Q4 are on, Q2 and Q3 are off, and conversely when the AC reactor current is negative, Q1 and Q4 are off, Q2 Q3 turns on. Therefore, the AC reactor current becomes a high-frequency current having positive and negative amplitudes.
[0016]
The component of the high-frequency current passing through the AC reactor 20 is removed by the AC filter capacitor 17, and a commercial frequency component synchronized with the system 18 is injected into the system 18 as an output current.
[0017]
As described above, according to this embodiment, the second inverter is switched at a high frequency, so that the energy can be always taken out regardless of the polarity of the current flowing in the current smoothing AC reactor. An inverter device can be realized.
[0018]
(Example 3)
Hereinafter, a third embodiment of the present invention will be described with reference to FIG. FIG. 5 is a waveform diagram showing the configuration of this embodiment. The components are the same as those in FIG.
[0019]
The operation of the grid-connected inverter device configured as described above will be described with reference to the waveform diagram of FIG. The high-frequency voltage generated on the secondary side of the high-frequency transformer 13 by the operation of the first inverter 12 is an inductive AC reactor, so that the current flowing through the AC reactor 20 is relative to the drive signal of the first inverter 12. Delayed phase. Therefore, if the second inverter 15 is operated at a high frequency while maintaining a constant phase lag with respect to the drive signal of the first inverter 12 during the commercial cycle, the switching is performed in the vicinity of zero of the AC reactor current. Therefore, the switching loss of the bidirectional switch 16 constituting the circuit 15 is reduced.
[0020]
As described above, according to this embodiment, the drive signal of the semiconductor switch constituting the first inverter and the drive signal of the bidirectional semiconductor switch constituting the second inverter are maintained with a constant phase difference. Thus, it is possible to provide a grid-connected inverter device that can simultaneously realize zero current switching and constant operation frequency with a simple configuration.
[0021]
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 differs from the circuit configuration of FIG. 3 in that the zero current detection means 40 is arranged on the secondary side of the high-frequency transformer 13 and the second inverter 15 is controlled by the zero current switching control means 41 using this output. This is the point. Components other than those described above are the same as those in the second embodiment, and a description thereof will be omitted.
[0022]
The operation of the grid-connected inverter device configured as described above will be described with reference to the waveform diagram of FIG. Since the output voltage of the high-frequency transformer 13 is sinusoidally modulated by the pulse width modulation (PWM) operation of the first inverter 12, the secondary voltage of the high-frequency transformer is positive with respect to the direction shown in the vicinity of the peak of the commercial cycle. The period is long.
[0023]
Conversely, in the vicinity of the valley, the high-frequency transformer secondary voltage has a longer negative period with respect to the illustrated direction. Therefore, the phase at which the AC reactor current passes through zero changes significantly during the commercial cycle. Therefore, the zero current detection means 40 arranged on the secondary side of the high-frequency transformer 13 detects the zero current timing of the AC reactor current that changes in the commercial cycle, and the zero current switching means 41 based on this output causes the zero current switching means 41 to be the second inverter. The bidirectional switch 16 constituting the switch 15 is switched at a high frequency.
[0024]
As described above, according to this embodiment, the zero current detecting means 40 for detecting the zero current of the secondary current of the high frequency transformer is provided, and the drive signal of the second inverter is synchronized with the output of the zero current detecting means. Since the switching loss of the bidirectional switch can be reduced to zero in principle, a grid-connected inverter device capable of reducing the loss can be provided.
[0025]
(Example 5)
Hereinafter, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a waveform diagram showing the configuration of this embodiment. The components are the same as those in FIG.
[0026]
The operation of the grid-connected inverter device configured as described above will be described with reference to the waveform diagram of FIG. The operating frequency of the AC reactor current is determined by the operating frequency of the first inverter 12. Since the operation of the second inverter 15 is performed at the timing of zero current of the AC reactor 20, the frequency may change as a result due to the influence of the dead time of each inverter. At that time, the operating frequency of the second inverter 15 is prioritized over the zero current switching, thereby eliminating the difference in the operating frequency between the first inverter 12 and the second inverter 15 and preventing the interference sound between the two inverters. .
[0027]
As described above, according to the present embodiment, it is possible to avoid generation of noise due to interference sound when the two inverters operate simultaneously by matching the operating frequencies of the second inverter and the first inverter. An inverter device can be realized.
[0028]
(Example 6)
The sixth embodiment of the present invention will be described below with reference to FIG. FIG. 9 is a block diagram showing the configuration of this embodiment. 9 differs from the circuit configuration of FIG. 3 in that a current limiting reactor 14 and a filter capacitor 60 are inserted between the high-frequency transformer 13 and the second inverter 15 as a low-pass filter configuration. Components other than those described above are the same as those in the third embodiment, and a description thereof will be omitted.
[0029]
The operation of the grid-connected inverter device configured as described above will be described with reference to FIG. Due to the difference between the rectangular wave-shaped high-frequency voltage generated on the secondary side of the high-frequency transformer and the system voltage, a current in a delayed phase flows through the current-limiting reactor 14. The high frequency component of the current limiting reactor current is removed by the filter capacitor 60, and the current input to the second inverter 15 becomes a commercial frequency sine wave. Here, the bidirectional switch 16 of the second inverter 15 is turned on / off according to the polarity of the system voltage. For example, when the system voltage is positive, the second inverter input current is positive in the direction shown in the figure. In Q1, Q1 and Q4 are turned on, and Q2 and Q3 are turned off.
[0030]
Further, when the system voltage is negative, Q2 and Q3 are turned on and Q1 and Q4 are turned off, so that a commercial frequency component synchronized with the system 18 is injected into the system 18 as an output current.
[0031]
As described above, according to the present embodiment, a current limiting reactor and a filter capacitor are inserted between the high-frequency transformer and the second inverter in a low-pass filter configuration, and the second inverter is switched at the commercial frequency. Since the switching loss can be reduced from the power loss, a small, light and inexpensive grid-connected inverter device can be provided.
[0032]
(Example 7)
The seventh embodiment of the present invention will be described below with reference to the drawings. FIG. 11 is a block diagram showing the configuration of this embodiment. 11 differs from the circuit configuration of FIG. 1 in that a relay is arranged between the second inverter and the system to enable independent output, and bidirectional between the current limiting reactor and the second inverter. The regenerative power processing means in which the switch and the electrolytic capacitor are connected in series is arranged. Components other than those described above are the same as those in the first embodiment, and a description thereof will be omitted.
[0033]
The operation of the grid interconnection inverter device configured as described above will be described with reference to the drawings. When the system 18 fails, the grid-connected inverter device is disconnected from the system and performs a sine wave voltage output self-sustaining operation. If a low power factor load such as a motor load is suddenly connected, a bidirectional switch that is a component of the regenerative power processing means 70 is turned on instantaneously, and a low impedance electrolytic capacitor is connected to the input stage of the second inverter 15. To regenerate power during the commercial cycle. When a resistive load that does not generate regenerative power is connected, the bidirectional switch is turned off.
[0034]
As described above, according to the present embodiment, the regenerative power processing means in which the electrolytic capacitor and the bidirectional switch are connected in series is arranged in parallel between the high-frequency transformer and the second inverter, and inductive and capacitive at the time of independent operation. When a low power factor load is connected, it is possible to provide a convenient grid-connected inverter device by instantly turning on a bidirectional switch.
[0035]
【The invention's effect】
As described above, according to the present invention, in a high frequency insulation type inverter, a bidirectional semiconductor switch is used for an inverter that converts a high frequency power of a high frequency transformer output into a commercial frequency power. This makes it possible to provide a grid-connected inverter that can be eliminated and that is significantly low loss, small, light, and inexpensive.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration of a grid-connected inverter device according to a first embodiment of the present invention. FIG. 2 is a waveform showing the operation of each part of the grid-connected inverter device according to the first embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of a grid-connected inverter device according to a second embodiment of the present invention. FIG. 4 shows the operation of each part of the grid-connected inverter device according to the second embodiment of the present invention. Waveform diagram [FIG. 5] 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] The configuration of the grid-connected inverter device according to the fourth embodiment of the present invention. FIG. 7 is a waveform diagram showing the operation of each part of the grid-connected inverter device according to the fourth embodiment of the present invention. FIG. 8 is a waveform diagram showing the operation of each section of the grid-connected inverter device according to the fifth embodiment of the present invention. FIG. 9 is a waveform chart showing the operation of the system according to the sixth embodiment of the present invention. FIG. 10 is a block diagram showing the configuration of the interconnection inverter device. FIG. 10 is a waveform diagram showing the operation of each part of the grid interconnection inverter device according to the sixth embodiment of the invention. FIG. 11 is the seventh embodiment of the invention. Block diagram showing the configuration of the grid-connected inverter device [FIG. 12] Block diagram showing the configuration of the conventional grid-connected inverter device [Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 DC power source 12 1st inverter 13 High frequency transformer 14 Current limiting reactor 15 2nd inverter 16 Bidirectional switch 17 AC filter capacitor 18 System | strain 20 AC reactor 40 Zero current detection means 41 Zero current switching means 60 Filter capacitor 70 Regenerative power processing means

Claims (2)

A high-frequency transformer, a first inverter arranged on the primary side of the high-frequency transformer that converts DC power into high-frequency power, and a current- limiting arranged on the secondary side of the high-frequency transformer that converts the high-frequency power into commercial power A reactor and a second inverter having a plurality of switching elements configured in a full bridge; the switching element of the second inverter is configured by a bidirectional switch; and the bidirectional switch of the second inverter is set to a polarity of a system voltage. in response system interconnection inverter device for converting the AC power of the high-frequency transformer and off. Regenerative power processing means having an electrolytic capacitor and a bidirectional switch connected in series is provided, and the regenerative power processing means is arranged in parallel with a high-frequency transformer and a second inverter, and the second inverter has a low power factor when operating independently. The grid interconnection inverter apparatus according to claim 1, wherein the bidirectional switch in the regenerative power processing means is turned on only when a load is connected .

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