JP2011061925A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power loss and noise and besides to downsize the structure of a device, in a power converter which performs DC/DC conversion. <P>SOLUTION: A plurality of single-phase inverters 20a, 20b, 20c, and 30d are connected in series to the latter part of a DC power source 1, and its latter part is equipped with a smoothing capacitor 6 which is connected via a smoothing diode 5, and a switch 4 for short-circuit which bypasses the smoothing capacitor 6. For the output of each of single-phase inverters 20a, 20b, 20c, and 30d, its control mode is switched according to the voltage of the DC power source 1, and in case that the output of each of single-phase inverters 20a, 20b, and 20c becomes zero in this control mode, all the semiconductor switch elements 21-24, 31-34, and 41-44 in the single-phase inverters are switched on to perform DC/DC conversion, making use of the charge/discharge of the DC power in the inverter circuit 20. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power conversion device that performs DC / DC conversion, for example, converting DC power of a DC power source such as a solar cell into DC power having a different voltage.

  2. Description of the Related Art A booster circuit as a conventional power converter includes a switching element, an inductor, a diode, and a smoothing electrolytic capacitor on the output side, and is a solar cell as a DC power source smoothed by the smoothing electrolytic capacitor on the input side Is boosted by turning on and off the switch element of the booster circuit, or is passed through without being boosted by the booster circuit, and is supplied to the inverter circuit in the subsequent stage. (For example, refer to Patent Document 1.)

Japanese Patent No. 3941346 (page 2-3, FIG. 1)

In such a conventional power conversion device, a large-capacity reactor is required as the output power capacity increases, and there is a problem that the device is increased in size and weight.
Further, when the switching element is switched at a high frequency in order to avoid this problem, there is a problem that a great loss and noise are generated.

  The present invention has been made to solve the above-described problems. In a power conversion device that performs direct current / direct current conversion, power loss and noise due to switching of a switch element are reduced, and the device configuration is compact and lightweight. An object of the present invention is to provide a power conversion device with high conversion efficiency.

  The power conversion device according to the present invention is configured by connecting AC sides of a plurality of single-phase inverters each having a semiconductor switch element and a DC voltage source in series, and connecting the AC side in series between output terminals of a DC power source. An inverter circuit that superimposes the output of each single-phase inverter on the output of the DC power supply, and a smoothing capacitor that is connected to the subsequent stage of the inverter circuit via a rectifier and smoothes the output of the inverter circuit And a short-circuit switch having one end connected to the inverter circuit and the other end connected to the negative electrode of the smoothing capacitor, and output control of the single-phase inverter that switches within a certain period and on-off control of the short-circuit switch In the output control mode consisting of a combination of the above, the single-phase inverter where the output becomes zero during the period when the output of the single-phase inverter becomes zero. All the converters of semiconductor switching elements are turned on, and performs use to DC / DC converter to charge and discharge of the DC voltage source in the inverter circuit.

According to the power conversion device of the present invention, since the DC / DC conversion is performed by using the charging / discharging of the capacitor that is the DC voltage source in the inverter circuit, a large-capacity reactor is not required, and a short circuit is achieved. The switch and the semiconductor switch element in the inverter circuit do not require high frequency switching.
Further, in the control mode in which the output of the single-phase inverter is zero, by turning on all the switch elements of the single-phase inverter, the current path flowing through the main circuit is dispersed.
For this reason, a power conversion device with high conversion efficiency in which reduction of power loss and noise and reduction in size and weight of the device configuration are promoted can be realized.

  The above-described and other objects, features, and effects of the present invention will become more apparent from the detailed description and the drawings in the following embodiments.

It is a main circuit block diagram of the power converter device which concerns on Embodiment 1 of this invention. It is a wave form diagram explaining operation | movement of the power converter device which concerns on Embodiment 1 of this invention. It is a circuit diagram for demonstrating operation | movement of the power converter device which concerns on Embodiment 1 of this invention. It is a block diagram of the power converter device which concerns on Embodiment 2 of this invention. It is a flowchart which shows the control action which concerns on Embodiment 2 of this invention. It is a block diagram of the power converter device which concerns on Embodiment 3 of this invention. It is a circuit diagram for demonstrating operation | movement of the power converter device which concerns on Embodiment 3 of this invention. It is a circuit diagram for demonstrating operation | movement of the power converter device which concerns on Embodiment 4 of this invention. It is a wave form diagram explaining operation | movement of the power converter device which concerns on Embodiment 4 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol shall show the same or an equivalent part.
Embodiment 1 FIG.
1 is a configuration diagram of a main circuit of a power conversion device according to Embodiment 1 of the present invention.
In FIG. 1, the AC side of an inverter circuit 20 is connected in series between output terminals of a DC power source 1 made of a solar cell or the like. The inverter circuit 20 is configured by connecting the AC sides of the first single-phase inverter 20a, the second single-phase inverter 20b, the third single-phase inverter 20c, and the fourth single-phase inverter 30d in series. The sum of the outputs of the inverters 20 a, 20 b, 20 c, and 30 d is superimposed on the DC voltage from the DC power supply 1 as the output of the inverter circuit 20.
The first, second, third, and fourth single-phase inverters 20a, 20b, 20c, and 30d constituting the inverter circuit 20 include semiconductor switch elements 21 to 24, 31 to 34, 41 to 44, 52, and a diode 56. , And a first capacitor 25, a second capacitor 35, a third capacitor 45, and a fourth capacitor 55 as a DC voltage source. Here, the semiconductor switch elements 21 to 24, 31 to 34, 41 to 44, and 52 are IGBTs (Insulated Gate Bipolar Transistors) in which diodes are connected in antiparallel, or MOSFETs in which diodes are built in between source and drain ( Metal Oxide Semiconductor Field Effect Transistor) is used.

Further, a short-circuit switch 4 and a rectifier diode 5 as a semiconductor element that determines conduction / non-connection are connected to the subsequent stage of the inverter circuit 20, and the anode side of the rectifier diode 5 is connected to the AC output line of the subsequent stage of the inverter circuit 20. The cathode side is connected to the positive electrode of the smoothing capacitor 6 at the output stage. Here, one end of the short-circuit switch 4 is connected to the negative electrode of the fourth capacitor in the single-phase inverter 30d connected to the last stage among the single-phase inverters constituting the inverter circuit 20, and the other end is connected to the smoothing capacitor 6. Connected to the negative electrode.
The shorting switch 4 may be a semiconductor switch element such as IGBT or MOSFET, or a mechanical switch.

The operation of the power conversion apparatus according to the first embodiment configured as described above will be described with reference to FIGS. Here, an operation is shown in which the voltage Vo of the smoothing capacitor 6 on the output side is boosted twice with respect to the voltage Vin of the DC power supply 1.
The first to fourth single-phase inverters are also referred to as bit1, bit2, bit3, and bit4, respectively, and the output voltages of the single-phase inverters are referred to as Vbit1, Vbit2, Vbit3, and Vbit4. S is a signal indicating the on / off state of the short-circuit switch 4.

  As shown in FIG. 2, the combined operation of the output control of each single-phase inverter 20a, 20b, 20c, 30d and the on / off control of the short-circuit switch 4 depends on the voltage of the DC power supply 1 from a plurality of preset control modes. The single-phase inverters bit1 to bit4 have a period in which the output voltage is positive and a period in which the output voltage is negative, or the output is output in any period. Is not generated, and the sum of the positive periods is equal to the sum of the negative periods.

In such a series of control cycles, as shown in FIG. 3, all the switch elements 21 to 24, 31 to 34 of the single-phase inverters bit 1, bit 2, and bit 3 in a period in which the output of the single-phase inverter is zero, 41-44 can be turned on.
Therefore, according to the power conversion device of the first embodiment, since the current path flowing through the main circuit is distributed, the loss of the main circuit can be reduced, and a high conversion efficiency can be obtained.

Embodiment 2. FIG.
FIG. 4 is a circuit configuration diagram showing a power conversion device according to Embodiment 2 of the present invention.
In the first embodiment, the method of turning on all the switch elements 21 to 24, 31 to 34, and 41 to 44 in the period in which the outputs of the single-phase inverters 20a, 20b, and 20c are zero has been described. In the power conversion device according to the second embodiment, as shown in FIG. 4, voltage detection is performed to detect capacitor voltages Vc1 to Vc4 of capacitors C1 to C4 that are DC voltage sources of the single-phase inverters 20a, 20b, 20c, and 30d. The input voltage detector 10 for detecting the input voltage of the inverter circuit 20, that is, the voltage Vin of the DC power supply 1, and the output voltage detector 15 for detecting the voltage Vo of the smoothing capacitor 6. The switching elements in the inverter circuit 20 and the shorting switch 4 are controlled by using the output signals of these voltage detectors as inputs. The control means is composed of, for example, a microcomputer or a digital signal processor.

The control operation will be described below based on the flowchart shown in FIG.
The input voltage Vin obtained from the DC power source 1 is monitored (step S1), and it is determined whether or not the input voltage Vin exceeds a predetermined input voltage set value V1 (step S2).
When the input voltage Vin exceeds the set voltage V1, the main circuit is activated.
At this time, one control mode is selected from among several operation modes (control modes) having different preset step-up ratios according to the input voltage Vin (step S3).

Next, the capacitor voltage Vc in the inverter circuit 20 is monitored (step S4).
The capacitor voltage Vc is the voltages Vc1, Vc2, and Vc3 of the first, second, and third capacitors 25, 35, and 45, respectively. Here, it is determined whether there is a period in which the outputs of the single-phase inverters 20a, 20b, 20c are zero in the operation mode selected previously (step S5). If there is a period in which the output is zero, the capacitor voltage Vc is It is determined whether it is smaller than the first voltage setting value V2 (step S6).

Then, the capacitor voltage Vc and the first voltage set value V2 are compared, and the discharge mode is determined until the corresponding capacitor voltage Vc falls below the first voltage set value V2 (step S7). A drive signal is output to each switch element, and the DC power (DC voltage source) in the inverter circuit 20 is discharged (step S8).

In step S5, if there is no period in which the outputs of the single-phase inverters 20a, 20b, and 20c are zero in the operation mode selected earlier, is the capacitor voltage Vc larger than the second voltage setting value V3? It is determined whether or not (step S9).
Here, the capacitor voltage Vc is the voltages Vc1, Vc2, and Vc3 of the first, second, and third capacitors 25, 35, and 45, and the second voltage setting value V3 is also the first, second, and third voltages. Are three voltage values V31, V32, and V33 set for the capacitors 25, 35, and 45, respectively.

  Then, each capacitor voltage Vc1, Vc2, Vc3 is compared with each voltage setting value V31, V32, V33, and charging is performed until each capacitor voltage Vc1, Vc2, Vc3 exceeds each voltage setting value V31, V32, V33. The mode is determined (step S10), a drive signal for turning on the shorting switch 4 is output, and a drive signal is output to each switch element in the inverter circuit 20 in accordance with the input voltage Vin from the DC power source 1. The DC power (DC voltage source) in the inverter circuit 20 is charged (step S11).

  Next, in step S6, the capacitor voltage Vc is compared with the first voltage setting value V2, and when the capacitor voltage Vc is smaller than the first voltage setting value V2, that is, the discharging of the capacitor voltage Vc is completed. Or in step S9, the voltages Vc1, Vc2, and Vc3 of the first, second, and third capacitors 25, 35, and 45 are compared with the respective voltage setting values V31, V32, and V33. When the capacitor voltages Vc1, Vc2, and Vc3 exceed the voltage setting values V31, V32, and V33, that is, the charging of the first, second, and third capacitors 25, 35, and 45 is completed. In this case, the capacitor voltage Vc4 of the fourth capacitor C4 in the inverter circuit 20 is monitored (step S12), and whether or not the fourth capacitor voltage Vc4 exceeds the third voltage set value V4. It is determined (step S13).

  Then, the fourth capacitor voltage Vc4 and the third voltage setting value V4 are compared, and the charging mode is determined until the capacitor voltage Vc4 exceeds the third voltage setting value V4 (step S10), and the inverter circuit 20 A drive signal is output to each of the switch elements to charge the DC power (DC voltage source) in the inverter circuit 20 (step S11).

  Next, in step S13, the fourth capacitor voltage Vc4 is compared with the third voltage setting value V4. When the fourth capacitor voltage Vc4 exceeds the third voltage setting value V4, that is, When the charging of the fourth capacitor 55 is completed, a drive signal for turning on and off the shorting switch 4 is output, and each switch element in the inverter circuit 20 is driven according to the input voltage Vin from the DC power supply 1. A signal is output to charge / discharge the DC power in the inverter circuit 20 (step S14).

Normally, when voltage remains in the capacitor, when all the semiconductor switching elements of the single-phase inverter are turned on, a short-circuit current flows through the semiconductor element until the charge of the capacitor disappears. Since the resistance value of the semiconductor element is as small as several mΩ, the value of the short-circuit current becomes large and the element may be destroyed due to heat generation.
In the second embodiment, when the first, second, and third capacitor voltages Vc1, Vc2, and Vc3 in the inverter circuit 20 satisfy a condition that is smaller than the set voltage value V2, the semiconductor switching element of each single-phase inverter Since all of 21-24, 31-34, 41-44 are turned on, the short-circuit current flowing out from the first, second, and third capacitors 25, 35, and 45 as the DC voltage source is minimized. It is possible to suppress the damage of the semiconductor element.

Embodiment 3 FIG.
FIG. 6 is a circuit configuration diagram showing a power conversion device according to Embodiment 3 of the present invention.
In the second embodiment, the case where the first, second, and third capacitor voltages in the inverter circuit 20 are controlled to be equal to or lower than the set value by detecting each capacitor voltage has been described. In the third embodiment, As shown in FIG. 6, discharging resistors 26, 36, 46 are provided in parallel with each capacitor that is a DC voltage source of a single-phase inverter.
In the operation mode using charging / discharging of the single-phase inverter, the sum of the periods in which the output voltage is positive and the sum of the periods in which the output voltage is negative are set to be equal and repeated at a constant period, so that the capacitor voltage is maintained. On the other hand, in the operation mode that does not use charging / discharging of the single-phase inverter, there is no charging period for the capacitor, so the time constant T = CR determined by the value R of the discharging resistors 26, 36, 46 and the value of the capacitor C And the capacitor voltage drops.

  In the third embodiment, as shown in FIG. 7, during the period when the output of the single-phase inverter is zero, normally (in the case where the capacitor is not completely discharged), Lo of the semiconductor switch elements included in the single-phase inverter. Only the (low potential) side is turned on (see FIG. 7 (a)), and at the same time when the output of the voltage detector (not shown) described in the second embodiment becomes lower than the set voltage (capacitor discharge). In this case, the Hi (high potential) side is also controlled to be turned on (see FIG. 7B), so that the control operation required for discharging the capacitor can be easily performed and the inverter circuit Since the power can be continuously supplied to the output side until the first, second, and third capacitor voltages within 20 are equal to or lower than the set value, an apparatus excellent in system operation can be obtained. it can.

Embodiment 4 FIG.
FIG. 8 is a circuit diagram for explaining the operation of the power conversion apparatus according to embodiment 4 of the present invention.
In the third embodiment, the case where the discharging resistors 26, 36, 46 are provided in parallel with the capacitors has been described. However, as shown in FIG. 8, the capacitor charging paths are connected to the single-phase inverters 20a, 20b, 20c. (FIG. 8A) and a discharge path (FIG. 8B) may be set.

That is, as shown in FIG. 9, the capacitor voltage can be charged by setting the ON time of the semiconductor switches 22 and 23 forming the discharge path to be shorter than that of the semiconductor switches 21 and 24 forming the charge path. . Further, the voltage of the capacitor can be discharged by setting the ON time of the semiconductor switches 22 and 23 forming the discharge path longer than that of the semiconductor switches 21 and 24 forming the charge path.
Therefore, according to the fourth embodiment, the charge / discharge of the capacitor voltage can be controlled by changing the conduction time ratio of the pair of upper and lower semiconductor switch elements included in the single-phase inverter within a certain period. it can.
As a result, since no additional parts such as a discharge resistor are required, the apparatus can be reduced in size and cost.
In addition, since the power consumed by the discharge resistor or the like is reduced, a device with high power conversion efficiency can be realized.

  In addition, although Embodiment 1-4 mentioned above demonstrated the case where a solar cell was used for DC power supply, this invention is not restricted to this, A storage battery and a constant voltage power supply may be sufficient, It goes without saying that other configurations and operations may be modified as long as they are within the range.

1 DC power supply, 4 shorting switch, 5 rectifier diode, 6 smoothing capacitor,
10 input voltage detector, 11 first voltage detector, 12 second voltage detector,
13 third voltage detector, 14 fourth voltage detector, 15 output voltage detector,
20 inverter circuit, 20a first single-phase inverter, 20b second single-phase inverter,
20c third single-phase inverter, 30d fourth single-phase inverter,
21-24, 31-34, 41-44, 52 semiconductor switch element,
25 first capacitor, 35 second capacitor, 45 third capacitor,
55 Fourth capacitor, 56 Rectifier diode, 26, 36, 46 Discharge resistor,
Vin DC power supply voltage (input voltage), Vbit1 first single-phase inverter output,
Vbit2 second single-phase inverter output, Vbit3 third single-phase inverter output,
Vbit4 4th single-phase inverter output,
Vc1 to Vc4 First to fourth capacitor voltages, Vo output voltage.

Claims (5)

  The AC side of a plurality of single-phase inverters each having a semiconductor switch element and a DC voltage source are connected in series, and the AC side is connected in series between output terminals of a DC power supply to output the output of each single-phase inverter. An inverter circuit that outputs the sum superimposed on the output of the DC power supply, a smoothing capacitor that is connected to the subsequent stage of the inverter circuit via a rectifier and smoothes the output of the inverter circuit, and one end connected to the inverter circuit An output control mode comprising a combination of output control of the single-phase inverter that switches within a certain period and on-off control of the short-circuit switch, the short-circuit switch having the other end connected to the negative electrode of the smoothing capacitor. In the period when the output of the single-phase inverter becomes zero, the semiconductor switching element of the single-phase inverter where the output becomes zero Te is the ON state, the power conversion device and performing DC / DC conversion by using charging and discharging of the DC voltage source in the inverter circuit.   The single-phase inverter includes a voltage detector that detects the voltage of the DC voltage source, and turns on all the semiconductor switch elements when the output of the voltage detector satisfies a condition smaller than a set voltage. The power conversion device according to claim 1.   In a period in which a discharge resistor is provided in parallel with the DC voltage source and the output of the single-phase inverter is zero, normally only the Lo (low potential) side of the semiconductor switch element of the single-phase inverter is turned on. The power converter according to claim 2, wherein when the output of the voltage detector becomes smaller than a set voltage, the Hi (high potential) side is also turned on.   2. The charge / discharge of the DC voltage source is controlled by controlling a conduction time ratio of a pair of upper and lower semiconductor switch elements included in the single-phase inverter within a certain period. 2. The power conversion device according to 2.   The said DC power supply is a solar cell, The power converter device of any one of Claims 1-4 characterized by the above-mentioned.

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