KR20110048002A - Grid-linked inverter device and grid-linked system - Google Patents

Abstract

PURPOSE: A grid connected inverter device and a grid connected system are provided to improve the reliability and simply overcome electromagnetic-interference noise related problems by suppressing current leakage. CONSTITUTION: A step-up/down voltage converter(2A) outputs an intermediate voltage by controlling an input voltage from direct current power supply. A full-bridge inverter(3A) converts the intermediate voltage into alternating current power in sinusoidal wave shape. The step-up/down voltage converter shapes a part of the sinusoidal wave shape corresponding to the alternating current power.

Description

GRID CONNECTED INVERTER DEVICE AND GRID CONNECTED SYSTEM

The present invention relates to a grid-linked inverter device and a grid-linked system that converts direct-current power from a direct-current power source into alternating-current power at a commercial frequency, and which can link the alternating current power to a power system.

Background Art Conventionally, a grid-linked inverter device capable of converting direct current power from a direct current power source such as a solar cell into alternating current power of a commercial frequency and linking the alternating current power to a power system is widely used.

In recent years, in order to realize the miniaturization and high efficiency of a grid-connected inverter device, the grid-linked inverter device of the circuit system (so-called transless system) which does not have an insulation transformer attracts attention.

The transformerless inverter system includes a voltage conversion circuit that always boosts the input voltage to a voltage higher than the grid voltage by high frequency switching and generates an intermediate voltage, and a waveform conversion that converts the intermediate voltage into AC power by high frequency switching. It has a circuit and outputs AC power to a power system.

In addition, since a voltage conversion circuit performs shaping of at least a portion of sinusoidal waveforms, a system-linked inverter device in which a part of high frequency switching can be omitted and a switching loss accompanying high frequency switching is reduced (Patent Documents 1 and 2) has been proposed. Reference).

Japanese Patent Laid-Open No. 2004-104963 Japanese Patent Laid-Open No. 2000-152661

However, in the system-linked inverter device described in Patent Documents 1 and 2, the voltage conversion circuit forms at least a part of sinusoidal waveforms so that the ground voltage of each of the positive and negative lines between the DC power supply and the voltage conversion circuit changes. do.

Here, a ground capacitance exists between a DC power supply such as a solar cell and the ground. Since the input / output is not electrically insulated from the transformerless system-linked inverter device, a leakage current flows through the ground capacitance when the ground voltage of each of the plus side line and the minus side line changes.

Accordingly, the system-linked inverter device described in Patent Documents 1 and 2 has a problem that the reliability from the safety surface and the security surface is not sufficient, and a countermeasure against noise such as EMI noise is required.

Therefore, an object of the present invention is to provide a grid-linked inverter device and a grid-linked system that can suppress a leakage current flowing through a ground capacitance, even when the voltage conversion circuit performs shaping of at least a portion of sinusoidal waveforms. do.

MEANS TO SOLVE THE PROBLEM In order to solve the subject mentioned above, this invention has the following characteristics. First, a characteristic of the grid-linked inverter device according to the present invention is to boost or step down the input voltage (input voltage Vi) from a DC power supply (DC power supply 1) and output an intermediate voltage (middle voltage Vd). A voltage conversion circuit (step-up converter 2A or step-up converter 2B) and a waveform conversion circuit (full bridge inverter 3A or 3B) for converting the intermediate voltage into sine wave AC power. The conversion circuit is a system-linked inverter device (system-linked inverter device 100A or 100B) which forms at least a portion of a sinusoidal waveform corresponding to the AC power, and the voltage conversion circuit includes a positive pole of the DC power supply and the The positive side circuit (plus side circuit 210A or 210B) provided on the positive side line (plus side line Lp) between the waveform converting circuits, and the minus between the negative pole of the DC power supply and the waveform converting circuit. It is a summary that the negative side circuit (minus side circuit 220A or 220B) provided on the side line (minus side line Ln) is provided, and the said positive side circuit and the said negative side circuit have a symmetrical circuit structure mutually. Shall be.

According to this aspect, the voltage conversion circuit for shaping at least a portion of the sinusoidal waveform corresponding to the AC power has a positive side circuit and a negative side circuit of symmetrical circuit configurations. The positive and negative circuits of symmetrical circuit configurations compensate for the positive and negative variations in the ground voltage so that the ground voltages of the positive and negative lines between the DC power supply and the voltage conversion circuit are constant. Is maintained. As a result, leakage current flowing through the ground capacitance can be suppressed, so that reliability from the safety and security surfaces can be improved, and measures such as EMI noise can be simplified.

In the system-linked inverter device according to the above-mentioned feature, the positive side circuit is configured by connecting a plurality of positive side circuit elements of different types in series on the positive side line, and the negative side circuit is configured as described above. On the negative side line, a plurality of negative side circuit elements of different types are connected in series, and are connected to the positive side circuit element which is n-th-numbered from the direct-current power supply side and n-th-numbered from the direct-current power supply side. The said negative side circuit element is a circuit element of the same kind. In addition, the same type of positive side circuit element and negative side circuit element are comprised using the circuit element of the same characteristic.

According to this aspect, by configuring the positive side circuit and the negative side circuit using circuit elements of the same type and the same characteristic, it is possible to balance the circuit characteristics of the positive side circuit and the negative side circuit, respectively, The ground voltage of each of the positive line and the negative line between the voltage conversion circuits can be further stabilized.

In the grid-linked inverter device according to the above feature, the plus-side circuit includes a first switching element (switching element 21a) and a first reactor (reactor 24a) connected to a rear end of the first switching element. And a first diode (diode 27a) connected to a rear end of the first reactor, wherein the negative side circuit includes a second switching element (switching element 21b) and a rear end of the second switching element. And a second reactor (reactor 24b) connected to the second reactor and a second diode (diode 27b) connected to the rear end of the second reactor. In addition, "back end" means the electric power system side, and "front end" means a DC power supply side.

According to such a system-linked inverter device, in a circuit configuration in which the voltage conversion circuit performs all shaping of a sine wave waveform corresponding to AC power, the positive side circuit and the negative side circuit can be symmetrical with each other. Likewise, leakage current flowing through the ground capacitance can be suppressed.

In the grid-linked inverter device according to the above aspect, a control unit (control unit 120A) for controlling the operation of the voltage conversion circuit is provided, and the control unit synchronizes the first switching element and the second switching element. Operate.

According to such a grid-connected inverter device, the positive side circuit and the negative side circuit are configured to be symmetrical to each other, and then the switching elements of the positive side circuit and the negative side circuit are operated synchronously, so that the positive side circuit and the negative side circuit, respectively The operation of can be made equal, and the ground voltage of each of the positive and negative lines between the DC power supply and the voltage conversion circuit can be further stabilized.

In the grid-linked inverter device according to the above feature, the plus side circuit includes a first reactor (reactor 24a) and a first diode (diode 27a) connected to a rear end of the first reactor. The negative side circuit includes a second reactor (reactor 24b) and a second diode (diode 27b) connected to a rear end of the second reactor.

According to such a grid-connected inverter device, in a circuit configuration in which a voltage conversion circuit performs shaping of a sine wave waveform corresponding to AC power, the positive side circuit and the negative side circuit can be symmetrical with each other. As described above, leakage current flowing through the ground capacitance can be suppressed.

A feature of the grid-coupling system according to the present invention is to provide a direct-current power supply (DC power supply 1) and a grid-linked inverter device according to the aforementioned feature.

According to this feature, the grid linkage system can be configured using the grid linkage inverter device capable of suppressing the leakage current flowing through the ground capacitance as described above, so that the reliability from the safety and security aspects can be improved. In addition, a system linkage system that can simplify measures such as EMI noise can be provided.

According to the present invention, even when the voltage conversion circuit has a circuit configuration for shaping at least a portion of sinusoidal waveforms, it is possible to provide a grid-linked inverter device and a grid-linked system capable of suppressing leakage current flowing through the ground capacitance.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the structure of the grid linkage system containing the grid linkage inverter device which concerns on 1st Embodiment.
2 is a waveform diagram illustrating the operation of the system-linked inverter device according to the first embodiment.
3 is a diagram illustrating a configuration of a grid linkage system including a grid linkage inverter device according to a second embodiment.
4 is a waveform diagram for describing an operation of a system-linked inverter device according to a second embodiment.
5 is a view for explaining a comparative example of the first embodiment;
6 is a view for explaining a comparative example of the second embodiment;

Next, the comparative example of 1st Embodiment, 2nd Embodiment, and Embodiment of this invention is demonstrated with reference to drawings. In the description of the drawings in the following embodiments, the same or similar parts are assigned the same or similar reference numerals.

[First Embodiment]

First, with reference to FIG. 1 and FIG. 2, 1st Embodiment of this invention is described.

FIG. 1: is a figure which shows the structure of the grid linkage system containing the grid linkage inverter device 100A which concerns on 1st Embodiment. 2 is a waveform diagram for explaining the operation of the grid-connected inverter device 100A.

As shown in FIG. 1, the grid linkage system includes a DC power supply 1, a grid linkage inverter device 100A, and a power grid 10. The DC power supply 1 is a distributed power supply that outputs DC power by power generation. In the following, a solar cell is illustrated as the DC power supply 1. The DC power supply 1 has a ground capacitance Cpv.

The grid-linked inverter device 100A converts the DC power from the DC power supply 1 into AC power of a commercial frequency (for example, 50 or 60 Hz). A load (not shown) installed on demand is connected between the grid-connected inverter device 100A and the power system 10. The grid-linked inverter device 100A performs linkage operation for supplying AC power to the load from both the grid-linked inverter device 100A and the power system 10.

The grid-connected inverter device 100A has a main circuit 110A and a control unit 120A for controlling the main circuit 110A. The main circuit 110A boosts and lowers the input voltage Vi from the DC power supply 1 and outputs the intermediate voltage Vd, and the AC voltage of the sinusoidal shape of the intermediate voltage Vd. It has the full bridge inverter 3A which converts into a. In the first embodiment, the step-up converter 2A configures a voltage conversion circuit. In the first embodiment, the full bridge inverter 3A constitutes a waveform conversion circuit.

The step-up / down converter 2A according to the first embodiment performs all shaping of a sine wave waveform corresponding to AC power (system voltage Vs). Here, the intermediate voltage Vd output by the step-up converter 2A is a sinusoidal standing wave (see FIG. 2F). The full bridge inverter 3A switches the polarity of the intermediate voltage Vd and outputs sine wave AC power.

The step-down converter 2A includes an input terminal capacitor 101, a positive side circuit 210A, a negative side circuit 220A, a diode 23, a switching element 25, a diode 26, and an intermediate stage capacitor 102. Has In the first embodiment, the insulated gate bipolar transistor (IGBT) is exemplified as the switching element 25, but a power MOSFET or the like may be used.

At the rear end of the DC power supply 1, the input terminal capacitor 101 has one end connected to the positive side line Lp between the positive pole of the DC power supply 1 and the full bridge inverter 3A, and the DC power supply 1 The other end is connected to the negative side line Ln between the negative pole of the () and the full bridge inverter 3A. The input terminal capacitor 101 smoothes the DC power from the DC power supply 1. In addition, "back end" means the electric power system side, and "front end" means a DC power supply side.

The positive side line Lp has one end connected to the positive pole side of the DC power supply 1 and the other end connected to one input side (plus side input) of the full bridge inverter 3A. One end of the negative side line Ln is connected to the negative pole side of the DC power supply 1, and the other end thereof is connected to the other input side of the full bridge inverter 3A (minus input).

The positive side circuit 210A is provided on the positive side line Lp. The minus side circuit 220A is provided on the minus side line Ln. The positive side circuit 210A and the negative side circuit 220A have a symmetric circuit configuration. Specifically, the positive side circuit 210A is configured by connecting a plurality of circuit elements of different types in series on the positive side line Lp. The negative side circuit 220A is configured by connecting a plurality of circuit elements of different types in series on the negative side line Ln. The circuit elements on the positive side that are counted from the DC power supply 1 side and connected to the nth side and the circuit elements on the negative side that are counted from the DC power source 1 side and connected to the nth number are the same kind of circuit elements (n is 1). Greater than). In addition, the symmetrical circuit configuration means symmetry on the circuit diagram, and the positions when the positive side circuit 210A and the negative side circuit 220A are actually disposed on the substrate need not be symmetrical.

The positive side circuit 210A is connected to the switching element 21a (first switching element), the reactor 24a (first reactor) connected to the rear end of the switching element 21a, and the rear end of the reactor 24a. Diode 27a (first diode).

One end (collector) of the switching element 21a is connected to the DC power supply 1 and the input terminal capacitor 101, and the other end (emitter) is connected to the reactor 24a. The diode 22a is anti-parallel connected to the switching element 21a. The switching element 21a performs high frequency switching according to the gate signal G1 from the control part 120A. One end (anode) of the diode 27a is connected to the reactor 24a, and the other end (cathode) of the diode 27a is connected to the full bridge inverter 3A.

The negative side circuit 220A is connected to the switching element 21b (second switching element), the reactor 24b (second reactor) connected to the rear end of the switching element 21b, and the rear end of the reactor 24b. Diode 27b (second diode).

As for the switching element 21b, one end (emitter) is connected to the DC power supply 1 and the input terminal capacitor 101, and the other end (collector) is connected to the reactor 24b. The diode 22b is anti-parallel connected to the switching element 21b. The switching element 21b performs high frequency switching according to the gate signal G1 from the control part 120A. That is, the switching element 21b is controlled by the gate signal G1 common to the switching element 21a. One end (cathode) of the diode 27b is connected to the reactor 24b, and the other end (anode) is connected to the full bridge inverter 3A.

In the present embodiment, the circuit elements on the positive side that are counted from the DC power supply 1 side and connected to the nth side and the circuit elements on the negative side that are counted from the DC power source 1 side and connected to the nth number are the same kind of circuit elements. Moreover, it is comprised using the circuit element of the same circuit characteristic.

For example, the circuit characteristics (ON voltage, switching speed, etc.) of each of the switching element 21a and the switching element 21b which are counted first from the DC power supply 1 side are equal. The circuit characteristics (inductance, etc.) of each of the reactor 24a and the reactor 24b connected secondly from the DC power supply 1 side are equal. The circuit characteristics (ON voltage, switching speed, etc.) of each of the diodes 27a and 27b connected to each other in the third direction from the DC power source 1 side are equal.

The reactors 24a and 24b may be configured by winding the windings corresponding to each of the reactors 24a and 24b on a common core in order to reduce the size.

The diode 23 is connected to the rear ends of the switching elements 21a and 21b. The diode 23 has one end (cathode) connected to a positive side line Lp between the switching element 21a and the reactor 24a, and has a negative side line (between the switching element 21b and the reactor 24b). The other end (cathode) is connected to Ln).

The switching element 25 is connected to the rear ends of the reactors 24a and 24b. The switching element 25 has one end (collector) connected to the positive side line Lp between the reactor 24a and the diode 27a, and the negative side line Ln between the reactor 24b and the diode 27b. ) Is connected to the other end (emitter). The diode 26 is anti-parallel connected to the switching element 25. The switching element 25 performs high frequency switching according to the gate signal G2 from the control part 120A.

The switching element 21a, the diode 22a, the diode 23, and the reactor 24a are used to step down the input voltage Vi and output the intermediate voltage Vd. The diode 23 and the reactor 24a smooth the output of which the voltage and current are interrupted by the switching of the switching element 21a.

FIG. 2A shows waveforms of the gate signal G1 input from the control unit 120A to the switching elements 21a and 21b. In addition, in FIG. 2, the section shown by hatching means the section of high frequency switching.

The switching element 21a controls the amplitude of the current waveform flowing through the reactor 24a by stepping down the input voltage Vi by high frequency switching and modulating the on time by the gate signal G1. On the other hand, the switching element 21b controls the amplitude of the current waveform flowing through the reactor 24b by high frequency switching in synchronization with the switching element 21a.

The reactor 24a, the switching element 25, the diode 26 and the diode 27a are used to boost the input voltage Vi and output the intermediate voltage Vd. The reactor 24a accumulates the boosted energy.

FIG. 2B shows a waveform of the gate signal G2 input from the control unit 120A to the switching element 25. The switching element 25 boosts the input voltage Vi by high frequency switching and modulates the on time by the gate signal G2, thereby controlling the amplitude of the current waveform flowing through the reactors 24a and 24b.

The switching elements 21a and 21b and the switching element 25 exclusively perform high frequency switching. Specifically, when the switching elements 21a and 21b switch at high frequency, the switching element 25 is turned off, and when the switching element 25 switches at high frequency, the switching elements 21a and 21b are turned on. do.

In the period in which the input voltage Vi is larger than the absolute value of the system voltage Vs, the controller 120A performs the step-down operation by switching the switching elements 21a and 21b at high frequency, and modulates the on time, thereby reacting the reactor 24a. , 24b) instantaneously control the amplitude of the current waveform. At this time, the switching element 25 is turned off. In the period in which the input voltage Vi is smaller than the absolute value of the system voltage Vs, the control unit 120A turns on the switching elements 21a and 21b and switches the switching element 25 to high frequency, thereby providing an input voltage Vi. Is boosted and the on-time is modulated to instantaneously control the amplitude of the current waveforms of the reactors 24a and 24b.

2 (f) shows the waveform of the intermediate voltage Vd. As shown in FIG. 2 (f), the high voltage component corresponding to the operating frequencies of the switching elements 21a and 21b and the switching element 25 is included in the intermediate voltage Vd output from the step-up converter 2A. Nested.

The intermediate stage capacitor 102 is connected to the rear ends of the diodes 27a and 27b. The intermediate stage capacitor 102 is used to remove high frequency components included in the intermediate voltage Vd. The intermediate stage capacitor 102 has one end connected to the positive side line Lp between the diode 27a and the full bridge inverter 3A, and the negative side line Ln between the diode 27a and the full bridge inverter 3A. Is connected to the other end. For example, the capacity of the intermediate stage capacitor 102 is about several tens of micrometers.

The full bridge inverter 3A switches the polarity of the intermediate voltage Vd and converts it to sine wave alternating current synchronized with the power system 10. The full bridge inverter 3A includes switching elements 31a to 31d connected with full bridges. In the first embodiment, the IGBTs are illustrated as the switching elements 31a to 31d, but may be a power MOSFET or the like.

The diodes 32a to 32d are antiparallel connected to the switching elements 31a to 31d, respectively. The switching elements 31a and 31d switch according to the gate signal G3 from the control part 120A. The switching elements 31b and 31c switch according to the gate signal G4 from the control part 120A. The power system 10 is connected to the connection point of the switching element 31a and the switching element 31b, and the connection point of the switching element 31c and the switching element 31d via a relay circuit (not shown).

2C shows waveforms of the gate signal G3 input from the control unit 120A to the switching elements 31a and 31d. FIG. 2D shows waveforms of the gate signal G4 input from the control unit 120A to the switching elements 31b and 31c. FIG. 2E shows waveforms of the input voltage Vi and the system voltage Vs, respectively. 2G shows the waveform of the output current Io. Fig. 2H shows the waveform of the input / output earth voltage. Specifically, the ground voltage Vp of the positive side line Lp between the DC power supply 1 and the boost converter 2A, and the negative side line between the DC power supply 1 and the boost converter 2A ( The ground voltage Vn of Ln, the ground voltage Vu of one line on the output side, and the ground voltage Vv of the other line on the output side are shown.

The switching elements 31a to 31d switch at a commercial frequency in synchronization with the plus and minus of the system voltage Vs, and the intermediate voltage Vd of the sinusoidal square wave shape corresponding to the commercial frequency obtained from the step-up converter 2A. ) Is converted into sinusoidal AC power synchronized with the power system 10.

As described above, according to the first embodiment, the step-up converter 2A has a positive side circuit 210A and a minus side circuit 220A having a symmetrical circuit configuration. By the positive side circuit 210A and the negative side circuit 220A of symmetrical circuit configurations, as shown in Fig. 2H, the positive side between the DC power supply 1 and the step-up converter 2A is shown. Variations in the ground voltages Vp and Vn of the line Lp and the negative side line Ln cancel each other by plus and minus to maintain the ground voltages Vp and Vn constant. As a result, the leakage current flowing through the ground capacitance Cpv can be suppressed.

In the first embodiment, the positive side circuit 210A and the negative side circuit 220A are configured using circuit elements having the same characteristics, so that the circuit characteristics of the positive side circuit 210A and the minus side circuit 220A are each. Can be equalized, and the ground voltages Vp and Vn can be further stabilized.

In addition, in the first embodiment, after the positive side circuit 210A and the negative side circuit 220A are symmetrical circuit configurations, the switching elements 21a of the positive side circuit 210A and the negative side circuit 220A, respectively, are provided. , 21b) in synchronization, the operation of each of the positive side circuit 210A and the negative side circuit 220A can be made equal, and the ground voltages Vp and Vn can be further stabilized.

Second Embodiment

Next, with reference to FIG. 3 and FIG. 4, 2nd Embodiment of this invention is described. In 2nd Embodiment, a mainly different point from 1st Embodiment is demonstrated.

FIG. 3: is a figure which shows the structure of the grid linkage system containing the grid linkage inverter device 100B which concerns on 2nd Embodiment. 4 is a waveform diagram illustrating the operation of the system-linked inverter device 100B.

The grid-linked inverter device 100B has a main circuit 110B and a control unit 120B for controlling the main circuit 110B. The main circuit 110B includes a boost converter 2B for boosting the input voltage Vi from the DC power supply 1 and outputting the intermediate voltage Vd, and converting the intermediate voltage Vd into sine wave-shaped AC power. It has a full bridge inverter 3B. In the second embodiment, the boost converter 2B constitutes a voltage conversion circuit. In the second embodiment, the full bridge inverter 3B constitutes a waveform conversion circuit.

The boost converter 2B according to the second embodiment performs shaping of a part of the sinusoidal waveform corresponding to the AC power (system voltage Vs). Here, the intermediate voltage Vd output by the boost converter 2B is a waveform which is partially convex (see FIG. 4E). The full bridge inverter 3B forms a sine wave waveform of the remaining portion and outputs sine wave-shaped AC power.

The boost converter 2B includes an input stage capacitor 101, a positive side circuit 210B, a negative side circuit 220B, a switching element 25, a diode 26, and an intermediate stage capacitor 102. Although the power MOSFET is illustrated as the switching element 25 in 2nd Embodiment, IGBT etc. may be sufficient. The switching element 25 performs high frequency switching according to the gate signal G1 from the control part 120B.

The plus side circuit 210B is provided on the plus side line Lp. The negative side circuit 220B is provided on the negative side line Ln. The positive side line Lp has one end connected to the positive pole side of the DC power supply 1, and the other end connected to one input side (plus side input) of the full bridge inverter 3B. One end of the negative line Ln is connected to the negative pole side of the DC power supply 1, and the other end thereof is connected to the other input side (the input of the negative side) of the full bridge inverter 3B.

The positive side circuit 210B and the negative side circuit 220B have a circuit configuration symmetrical with each other. Specifically, the positive side circuit 210B is configured by connecting a plurality of circuit elements of different types in series on the positive side line Lp. The negative side circuit 220B is configured by connecting a plurality of circuit elements of different types in series on the negative side line Ln. The circuit elements on the positive side that are counted from the DC power supply 1 side and connected to the nth side and the circuit elements on the negative side that are counted from the DC power source 1 side and connected to the nth number are the same kind of circuit elements (n is 1). Greater than). In addition, the symmetrical circuit configuration means symmetry on the circuit diagram, and the positions when the positive side circuit 210B and the negative side circuit 220B are actually disposed on the substrate need not be symmetrical.

The positive side circuit 210B includes a reactor 24a (first reactor) and a diode 27a (first diode) connected to the rear end of the reactor 24a. The negative side circuit 220B includes a reactor 24b (second reactor) and a diode 27b (second diode) connected to the rear end of the reactor 24b.

The positive side circuit 210B and the negative side circuit 220B are configured using circuit elements having the same characteristics. The circuit characteristics (inductance, etc.) of each of the reactor 24a and the reactor 24b connected to each other by counting from the DC power supply 1 side are equal. The circuit characteristics (ON voltage, switching speed, etc.) of each of the diodes 27a and 27b connected secondly from the DC power supply 1 side are equal. The reactors 24a and 24b may be configured by winding the windings corresponding to each of the reactors 24a and 24b on a common core in order to reduce the size.

4A shows waveforms of the gate signal G1 input to the switching element 25 from the control unit 120B. In addition, in FIG. 4, the section shown by hatching means the section of high frequency switching. 4D illustrates waveforms of the input voltage Vi and the system voltage Vs, respectively.

Step-up converter 2B performs step-up for a certain period centering on the point of time of peak voltage of system voltage Vs, and other periods, specifically, the absolute value of system voltage Vs is input voltage Vi. In a period smaller than), the boosting is not performed.

FIG. 4E shows the waveform of the intermediate voltage Vd. The intermediate voltage Vd becomes a waveform in which the boosted section is partially convex. The full bridge inverter 3B is shaped for the sine wave waveform of the remaining portion.

The full bridge inverter 3B has the same circuit configuration as that of the first embodiment except that IGBT is used as the switching elements 31a to 31d. However, not only IGBT but power MOSFET etc. may be used.

4B illustrates waveforms of the gate signal G2 input from the control unit 120B to the switching elements 31a and 31d. FIG. 4C shows waveforms of the gate signal G3 input from the control unit 120B to the switching elements 31b and 31c.

The boost converter 2B and the full bridge inverter 3B alternately perform high frequency switching, and the boost converter 2B and the full bridge inverter 3B form a sine wave waveform. The sinusoidal waveform is formed by a circuit which performs high frequency switching. In addition, when the boost converter 2B is performing high frequency switching (forming sine wave waveform), the full bridge inverter 3B switches polarity as needed, and the full bridge inverter 3B has a high frequency. In the case of switching (when forming a sinusoidal waveform), the boost converter 2B stops the boosting operation (turns off the switching element 25).

4F shows waveforms of the output voltage Vo output by the full bridge inverter 3B. The high frequency component corresponding to the high frequency switching by the full bridge inverter 3B is superimposed on the output voltage Vo.

The filter circuit 4 is connected to the rear end of the full bridge inverter 3B. The filter circuit 4 includes a switching element 41a, a diode 42a, a switching element 41b, a diode 42b, a reactor 43a, a reactor 43b, and a capacitor 44. The filter circuit 4 removes and outputs the high frequency component contained in the output (output voltage Vo) from the full bridge inverter 3B.

Fig. 4G shows the waveform of the output current Io. Fig. 4H shows the waveform of the input / output earth voltage. Specifically, the ground voltage Vp of the positive side line Lp between the DC power supply 1 and the boost converter 2B, and the negative side line Ln between the DC power supply 1 and the boost converter 2B. The ground voltage Vn, the ground voltage Vu of one line on the output side, and the ground voltage Vv of the other line on the output side are shown.

As described above, in the second embodiment, the positive side circuit 210B and the negative side circuit 220B are connected to each other in the circuit configuration in which the boost converter 2B forms a part of the sinusoidal waveform corresponding to the AC power. By setting the circuit configuration to be symmetrical, the leakage current flowing through the ground capacitance Cpv can be suppressed as in the first embodiment.

In addition, in the second embodiment, the positive side circuit 210B and the negative side circuit 220B are configured using circuit elements having the same characteristics, so that the balance between the positive and negative circuit characteristics can be equalized, and the earth voltage (Vp, Vn) can be further stabilized.

[Comparative Example]

Next, in order to clarify the effects obtained by the first embodiment and the second embodiment, a comparative example of the first embodiment and the second embodiment will be described with reference to FIGS. 5 and 6.

5 is a diagram for explaining a comparative example of the first embodiment. In this comparative example, the step-up converter 2A 'does not have the negative side circuit 220A described in the first embodiment. The rest of the configuration is the same as in the first embodiment. As shown in Fig. 5, in the circuit configuration in which the step-up converter 2A 'does not have the minus-side circuit 220A, the positive side line Lp between the DC power supply 1 and the step-up converter 2A'. ) And the ground voltages Vp and Vn of the negative side line Ln are varied. For this reason, a leakage current flows through earth capacitance Cpv. On the other hand, in the first embodiment described above, as shown in FIG. 1, the ground voltages Vp and Vn are kept constant, and the leakage current can be suppressed.

6 is a diagram for explaining a comparative example of the second embodiment. In this comparative example, the boost converter 2B 'does not have the negative side circuit 220B described in the second embodiment. The rest of the configuration is the same as in the second embodiment. As shown in Fig. 6, in the circuit configuration in which the boost converter 2B 'does not have the negative side circuit 220B, the positive side line Lp between the DC power supply 1 and the boost converter 2B' and The ground voltages Vp and Vn of each of the negative side lines Ln change. For this reason, a leakage current flows through earth capacitance Cpv. On the other hand, in 2nd Embodiment mentioned above, as shown in FIG. 3, the ground voltages Vp and Vn are kept constant, and leakage current can be suppressed.

[Other Embodiments]

As mentioned above, although this invention was described by embodiment, the description and drawing which form a part of this indication should not be understood as limiting this invention. Various alternative embodiments, examples, and operational techniques will be apparent to those skilled in the art from this disclosure.

For example, in each embodiment mentioned above, although the solar cell was illustrated as the DC power supply 1, what is necessary is just a DC power supply which has earth capacitance Cpv, and it is not limited to a solar cell.

In addition, in each embodiment mentioned above, the case using the step-up converter 2A or the step-up converter 2B as a voltage conversion circuit was illustrated. However, in the case where the input voltage Vi is higher than the system voltage Vs, the step-down converter may be used as the voltage conversion circuit. The step-down converter steps down the input voltage Vi and outputs the intermediate voltage Vd.

As described above, it should be understood that the present invention includes various embodiments which are not described herein. Therefore, this invention is limited only by the invention specific matters of a reasonable claim from this indication.

Cpv: Earth capacitance
Ln: minus track
Lp: Plus side track
1: DC power
2A: Step-Up Converter
2B: Step-up Converter
3A, 3B: Full Bridge Inverter
4: filter circuit
10: power system
21a, 21b, 25, 31a to 31d, 41a, 41b: switching element
22a, 22b, 23, 26, 27a, 27b, 32a to 32d, 42a, 42b: diode
24a, 24b, 43a, 43b: reactor
44: condenser
100A, 100B: Grid Connected Inverter Unit
101: input stage capacitor
102: intermediate stage capacitor
110A, 110B: main circuit
120A, 120B: control unit
210A, 210B: plus side circuit
220A, 220B: minus side circuit

Claims (6)

A voltage conversion circuit for boosting or stepping down an input voltage from a DC power supply and outputting an intermediate voltage;
It has a waveform conversion circuit which converts the said intermediate voltage into the sine wave shape AC power,
The voltage conversion circuit is a system-linked inverter device for shaping at least a portion of a sine wave waveform corresponding to the AC power,
The voltage conversion circuit,
A positive side circuit provided on a positive side line between the positive pole of the DC power supply and the waveform conversion circuit;
And a negative side circuit provided on a negative side line between the negative pole of said DC power supply and said waveform conversion circuit,
The positive side circuit and the negative side circuit have a circuit configuration that is symmetric with each other. The positive side circuit according to claim 1, wherein the positive side circuit is configured by connecting a plurality of positive side circuit elements of different types in series on the positive side line,
The negative side circuit is configured by connecting a plurality of negative side circuit elements of different types in series on the negative side line,
The positive-side circuit element connected to the n-th number from the DC power supply side and the negative-side circuit element connected to the n-th number from the DC power supply side are circuit elements of the same kind. The circuit of claim 1 or 2, wherein the plus side circuit comprises:
A first switching element,
A first reactor connected to a rear end of the first switching element,
A first diode connected to a rear end of the first reactor,
The negative side circuit,
A second switching element,
A second reactor connected to a rear end of the second switching element,
And a second diode connected to a rear end of the second reactor. 4. The control apparatus according to claim 3, further comprising a control unit for controlling the operation of the voltage conversion circuit.
And the control unit operates the first switching element and the second switching element in synchronization with each other. The circuit of claim 1 or 2, wherein the plus side circuit comprises:
The first reactor,
A first diode connected to a rear end of the first reactor,
The negative side circuit,
The second reactor,
And a second diode connected to a rear end of the second reactor. With DC power supply,
A grid linkage system comprising the grid linkage inverter device according to claim 1.

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