JP2006238629A - Power conversion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve efficiency by reducing the loss of a power conversion apparatus that supplies AC electric power to a load or a system by performing AC conversion after stepping up a photovoltaic voltage. <P>SOLUTION: An inverter unit 1 comprises single-phase inverters 1B-INV, 2B-INV, 3B-INV, into which electric power from DC power supplies V<SB>1B</SB>, V<SB>2B</SB>, V<SB>3B</SB>having the voltage ratio of 1:3:9 is input, respectively. The AC sides of the unit 1 are connected in series, and an output voltage controlled in gradation according to the total sum of each generated voltage. Also, the DC power supply V<SB>3B</SB>of the maximum voltage is formed by stepping up the photovoltaic voltage V<SB>O</SB>with a chopper circuit 3. The loss related to the stepping-up is reduced by stopping the stepping-up operation of the chopper circuit 3 when the V<SB>O</SB>exceeds a prescribed voltage V<SB>m1</SB>(195 V) and by bypassing a reactor 3b and a diode 3c inside the chopper circuit 3 with a relay 7a connected in parallel. Furthermore, conduction loss of the components inside the chopper circuit 3 is eliminated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power conversion device that converts DC power into AC power, and more particularly to a power conversion device that is used in a power conditioner or the like that connects a distributed power source to a system.

In a conventional power conditioner, for example, as shown in a solar power conditioner, the voltage is boosted using a chopper from a distributed power source that is a solar cell, and a PWM controlled inverter is inserted in the subsequent stage to generate an output AC voltage. is doing.
The basic operation of such a conventional power conditioner will be described below. The DC power output from the solar cell drives the internal control power supply of the power conditioner, and the internal circuit can operate. Using a chopper circuit, the voltage of the solar cell is boosted to a voltage required to connect to the grid. The inverter unit is composed of four switches, and performs PWM switching so that the output current has a phase synchronized with the system voltage. In this way, a strip-like waveform is output to the output, the output voltage is controlled by changing the output time ratio, the output voltage is averaged by the smoothing filter provided on the output side, and the system is AC Electric power is output (for example, refer nonpatent literature 1).

"Development of solar power conditioner type KP40F" OMRON TECHNICS Vol.42 No.2 (Vol.142) 2002

  In the conventional power conditioner that links the solar voltage to the system, the maximum value of the output voltage of the inverter is determined by the magnitude of the boosted voltage by the chopper. For this reason, for example, when outputting an AC voltage of 200 V, the boosted DC voltage needs to be 282 V or higher, and is usually set higher with a margin. The output voltage of the solar voltage is usually about 200 V or less, and needs to be boosted to 282 V or more as described above. When the boosting rate is increased, the loss of the switching elements and diodes in the chopper portion is increased, and there is a problem that the efficiency of the entire power conditioner is lowered.

  The present invention was made to solve the above-described problems, and in a power conversion device that converts electric power from a direct-current power source such as sunlight into alternating current and outputs the alternating current to a system or a load, each unit The purpose is to improve the conversion efficiency by reducing the loss.

  According to a first power converter of the present invention, a plurality of AC sides of a single-phase inverter that converts DC power of a DC power source into AC power are connected in series, and a predetermined combination selected from the plurality of single-phase inverters is used. The gradation of the output voltage is controlled by the sum of the generated voltages. The plurality of DC power sources that are input to the single-phase inverters are composed of a first DC power source having the maximum voltage and other one or a plurality of second DC power sources. The voltage of the third DC power source Is boosted, and the output voltage is used as the first DC power supply, and the bypass circuit bypasses the voltage circuit. When the voltage of the third DC power source exceeds a predetermined voltage, the on / off operation of the switch in the booster circuit is stopped to stop the booster operation, and the booster circuit is bypassed by the bypass circuit. is there.

  The power conversion device according to the present invention can output a voltage higher than the output voltage of the booster circuit that boosts the voltage of the third DC power supply, and can reduce the boosting rate of the booster circuit and reduce the loss. Further, when the voltage of the third DC power supply exceeds a predetermined voltage, the on / off operation of the switch in the booster circuit is stopped to stop the booster operation, and the bypass circuit is bypassed by the bypass circuit. Loss is greatly reduced, and conduction loss of components constituting the booster circuit can be eliminated even when boosting is stopped, and a power conversion device with high conversion efficiency can be obtained.

Embodiment 1 FIG.
Hereinafter, a power conversion apparatus (hereinafter referred to as a power conditioner) according to Embodiment 1 of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating a power conditioner according to Embodiment 1 of the present invention. As shown in Fig. 1 (a), an inverter unit that is a single-phase multiple converter by connecting the AC sides of multiple (in this case, three) single-phase inverters 3B-INV, 2B-INV, and 1B-INV in series 1 is constructed. In addition, a chopper circuit 3 as a booster circuit including a switching element (hereinafter referred to as a switch) 3a such as an IGBT 3a, a reactor 3b, and a diode 3c is installed at the subsequent stage of the direct current power source 2 using sunlight as a third direct current power source. ing. The chopper circuit 3 boosts a DC voltage V _O obtained in the DC power supply 2, voltage V _C to be charged in the smoothing capacitor 4 serving as a first DC power source is obtained. Further, in order to bypass the chopper circuit 3 when the boosting is stopped, for example, a bypass circuit 7 including a relay 7 a is connected in parallel to the chopper circuit 3.

Each single-phase inverter 3B-INV, 2B-INV, 1B-INV is composed of a plurality of self-extinguishing semiconductor switching elements such as IGBTs having diodes connected in antiparallel as shown in FIG. 1 (b). Then, the DC power is converted into AC power and output, and the DC power supply portion of each input is connected by the bidirectional DC / DC converter 5.
These single-phase inverters 3B-INV, 2B-INV, and 1B-INV can generate positive and negative and zero voltages as outputs, and the inverter unit 1 generates a voltage _VA as a sum total of these generated voltages. Output by gradation control. The output voltage V _A is smoothed by the smoothing filter 6 including the reactor 6a and the capacitor 6b, and the AC voltage V _out is supplied to the system or the load.

In addition, the DC power source (first DC power source) serving as the input of 3B-INV corresponds to the smoothing capacitor 4, and the voltage V _3B (= V _C ) of other single-phase inverters 2B-INV and 1B-INV It is controlled by the DC / DC converter 5 so that the voltages V _2B and V _1B are larger than the voltages V _2B and V _1B of the direct-current power supply (second DC power supply) as an input, and V _1B , V _2B and V _3B have a predetermined voltage ratio. . The DC / DC converter 5 supplies surplus or deficient energy to each other while keeping the voltage ratio of the DC power sources V _1B , V _2B , and V _3B of each inverter constant.
Since V _1B , V _2B , and V _3B indicate the DC power supply voltages of the inverters 1B-INV, 2B-INV, and 3B-INV, the DC power supply V _1B , It describes as DC power supply _V2B and DC power supply _V3B .
Here, the relationship between V _1B , V _2B , and V _3B is 1: 3: 9. At this time, as shown in FIG. 2A, if the output patterns of the three inverters 1B-INV, 2B-INV, and 3B-INV are combined well, the output voltage V _A of the inverter unit 1 is 14th floor of 0-13. Selectable output voltage. As a result, as shown in FIG. 2B, an output voltage V _A having an approximately sinusoidal output voltage waveform 11 is obtained and input to the smoothing filter 6. Furthermore, as shown in FIG. 3, the voltage waveform can be controlled with higher accuracy by using PWM control at each gradation level. In the output pattern of each inverter shown in FIG. 2A, 1 represents positive voltage generation, -1 represents negative voltage generation, and 0 represents zero voltage generation.

The relationship between V _1B , V _2B , and V _3B may be other than 1: 3: 9, and the output voltage V _A has a continuous gradation level according to various patterns from 1: 2: 4 to 1: 3: 9. Change is possible. In each case, the relationship between the output pattern of each inverter 1B-INV, 2B-INV, 3B-INV and the gradation level of the output voltage _VA of the inverter unit 1 in which they are connected in series is shown in FIGS. Shown in the logical table. Of these, in the case of 1: 3: 9, the number of levels is the largest and a highly accurate output voltage waveform can be expected. In addition, if PWM control is used in combination at each gradation level, the voltage waveform can be controlled with higher accuracy. In order to apply PWM control to the voltage output method at each gradation level, depending on the voltage relationship of V _1B , V _2B , and V _3B , it is necessary to apply PWM control to the outputs of a plurality of single-phase inverters.

When PWM control is assumed, the voltage of the DC power supply V _1B may be larger than the voltage relationship shown in FIG. 4, and as shown in FIG. In addition, since each gradation level overlaps by ΔV, more continuous waveform output is possible. Conditions Ax to Jx corresponding to the logic tables A to J of FIG. 4 are shown in FIG. For example, under condition Jx, ΔV = V _1B −V _3B / 9.

By the way, the maximum output voltage required for the AC output of 200 V is about 282 V, and the output voltage V _A of the inverter unit 1 can output up to V _1B + V _2B + V _3B . For this reason, if V _1B + V _2B + V _3B is about 282V or more, the power conditioner can output 200V AC. V _1B + V _2B + V _3B is larger than V _3B which is a voltage boosted by the chopper circuit 3. For example, when the relationship between V _1B , V _2B and V _3B is 1: 3: 9, 13/9 of V _3B Doubled. That is, when V _3B is about 195 V or more, V _1B + V _2B + V _3B is 282 V or more, which is an AC output condition.
As described above, in order to obtain a predetermined AC output _Vout when the relationship between V _1B , V _2B , and V _3B is 1: 3: 9, the chopper circuit 3 is operated so that V _3B becomes about 195V or more. It is necessary to let

The operation of the chopper circuit 3 of such a power conditioner will be described below.
In the chopper circuit 3, the DC voltage (solar voltage) V _O obtained by the input DC power source 2 turns on and off the IGBT switch 3a up to a predetermined voltage V _m1 (195 V) and boosts the voltage to the voltage V _m1 . During this time, the relay 7a of the bypass circuit 7 is opened. When the voltage V _m1 is exceeded, the IGBT switch 3a is stopped. At this time, the relay 7a of the bypass circuit 7 is closed and a current is supplied to the bypass circuit 7 to bypass the reactor 3b and the diode 3c of the chopper circuit 3.

FIG. 6 shows the operating voltage with respect to the sunlight voltage V _O in the chopper circuit 3 and the estimated efficiency value at that time.
As shown, the range solar light voltage V _O is less than or equal to the predetermined voltage V _m1, because the chopper circuit 3 that boosts the output voltage V _3B is constant voltage V _m1, increased solar light voltage V _O At the same time, the step-up rate is lowered, and the efficiency of the chopper circuit 3 is improved. When the solar voltage V _O exceeds the predetermined voltage V _m1 , the boosting operation is stopped, the relay 7a of the bypass circuit 7 is closed, and a current flows to the bypass circuit 7 side, so that there is almost no loss. For this reason, the efficiency of the solar voltage V _O suddenly increases with the voltage V _m1 as a boundary.
The predetermined voltage V _m1 for stopping the boosting operation may be about 195 V or more, but the loss of the chopper circuit 3 can be further reduced by using a lower voltage. After stopping the boosting operation, not only the loss is greatly reduced by stopping the IGBT switch 3a, but also the conduction loss of the reactor 3b and the diode 3c can be eliminated by bypassing the reactor 3b and the diode 3c in the chopper circuit 3. Thus, the loss in the chopper circuit 3 is almost eliminated.

In this embodiment, the AC of the single-phase inverter 3B-INV to the DC voltage V _3B boosted solar voltage V _O by the chopper circuit 3 and a DC source, the other single-phase inverters 2B-INV, and 1B-INV The inverters were connected in series, and the power conditioner was configured to obtain the output voltage by the sum of the voltages generated by each inverter. Further, the DC power sources V _2B and V _{1B that} are input to the single-phase inverters 2B-INV and 1B-INV are connected to the DC power source V _3B via the DC / DC converter 5 and are voltage-controlled, so that the chopper circuit 3 may be generated only a DC power source V _3B from solar light voltage V _O, an efficient device configuration. In the power conditioner configured as described above, a voltage higher than the DC voltage V _3B boosted by the chopper circuit 3 can be output, the boost rate of the chopper circuit 3 can be reduced, and the loss can be reduced.
Further, when the operating region of the voltage V _3B is set to a voltage region lower than the maximum value of the output voltage of the power conditioner, the boosting rate of the chopper circuit 3 can be reliably reduced and the loss can be reduced.
Further, when the solar voltage V _O exceeds the predetermined voltage V _m1 , the boosting operation is stopped and the chopper circuit 3 is bypassed by the bypass circuit 7, so that the loss can be almost eliminated and the power conditioner having high conversion efficiency. Is obtained.

Embodiment 2. FIG.
Details of the bypass circuit 7 in the first embodiment will be described below.
The bypass circuit 7 includes a relay 7a, and bypasses one or both of the reactor 3b and the diode 3c connected in series in the chopper circuit 3.
FIG. 7A shows the relay 7a bypassing the reactor 3b and the diode 3c as shown in the first embodiment, and FIG. 7B shows the relay 7a bypassing only the diode 3c. 7 (c) shows the relay 7a that bypasses only the reactor 3b.
The relay 7a is connected in parallel with a self-extinguishing semiconductor switch 7b. Since the relay 7a is generally opened at zero current or opened at a low voltage, the direct current is difficult to cut off. However, the relay 7a can be easily cut off by providing the semiconductor switch 7b in parallel. In that case, the semiconductor switch 7b is turned on simultaneously with opening the relay 7a, and the current is once transferred to the semiconductor switch 7b. As a result, the current flowing through the relay 7a is cut off, and then the semiconductor switch 7b is turned off.

In any case, when the solar voltage V _O exceeds the predetermined voltage V _m1 , the IGBT switch 3a is stopped to stop the boosting operation, the relay 7a of the bypass circuit 7 is closed, and a current flows to the bypass circuit 7 side. .
In the case of FIG. 7A, by bypassing the reactor 3b and the diode 3c in the chopper circuit 3, the conduction loss of the reactor 3b and the diode 3c can be eliminated, and the efficiency of the entire power conditioner is increased.
In the case of FIG. 7B, by bypassing only the diode 3c in the chopper circuit 3, the conduction loss of the diode 3c can be eliminated, and the efficiency of the entire power conditioner is increased. In this case, since reactor 3b is not bypassed, reactor 3b can be used as a filter.

7 (a) and 7 (b), in order to bypass the diode 3c, when the DC power source V _3B becomes higher than the solar voltage V _O , the current flows backward or further reverses to the solar panel that is the DC power source 2. There is a risk of voltage damage and panel damage. For this reason, the current flowing through the relay 7a is detected, and when the current falls below a certain value, the relay 7a is opened and switched to the current path via the reactor 3b and the diode 3c. In this way, the relay 7a is opened to enable the function of the diode 3c, thereby providing a backflow prevention and further a solar panel reverse voltage protection function.
When the relay 7a is opened, even if a reverse current has already occurred due to a detection delay or the like, the relay 7a can be reliably interrupted by temporarily transferring the current to the semiconductor switch 7b.

  In the case of FIG. 7C, by bypassing only the reactor 3b in the chopper circuit 3, the conduction loss of the reactor 3b can be eliminated, and the efficiency of the entire power conditioner is increased. Moreover, since the diode 3c is not bypassed, the reverse flow can be prevented and the solar panel reverse voltage can be protected by the diode 3c, and the reliability can be easily improved. In this case, the relay 7a can be cut off without providing the semiconductor switch 7b. However, the provision of the semiconductor switch 7b can also cut off even in the case of an abnormality of the diode 3c.

It is a schematic block diagram which shows the power conditioner by Embodiment 1 of this invention. It is a figure which shows the output pattern and output voltage waveform of each single phase inverter by Embodiment 1 of this invention. It is a figure which shows the output voltage waveform in the PWM control of the inverter by Embodiment 1 of this invention. It is a figure which shows the relationship between the output pattern and output gradation of each single phase inverter by Embodiment 1 of this invention. It is a figure which shows the DC voltage conditions and output voltage waveform of each single phase inverter by Embodiment 1 of this invention. It is a figure which shows operation | movement of the chopper circuit by Embodiment 1 of this invention. It is a figure which shows the structure of the bypass circuit by Embodiment 2 of this invention.

Explanation of symbols

2 third DC power supply (sunlight), 3 chopper circuit as booster circuit,
3a switch, 4 smoothing capacitor as the first DC power supply,
5, 5a, 5b DC / DC converter, 7 bypass circuit, 7a relay,
1B-INV, 2B-INV, 2Ba-INV, 3B-INV Single-phase inverter.

Claims (7)

Connect the AC side of a single-phase inverter that converts DC power of the DC power supply to AC power in series, and gradation the output voltage by the sum of each generated voltage by a predetermined combination selected from the above-mentioned single-phase inverters In the power converter to control,
The plurality of DC power sources serving as inputs of the single-phase inverters are composed of a first DC power source having a maximum voltage and other one or a plurality of second DC power sources,
A voltage boosting circuit that boosts the voltage of a third DC power supply and uses the output voltage as the first DC power supply; and a bypass circuit that bypasses the voltage boosting circuit,
When the voltage of the third DC power source exceeds a predetermined voltage, the on / off operation of the switch in the booster circuit is stopped to stop the booster operation, and the booster circuit is bypassed by the bypass circuit. Power converter. The step-up circuit includes a reactor, a rectifying element, and the switch, and the bypass circuit bypasses both the reactor and the rectifying element connected in series or only the rectifying element. The power conversion device according to claim 1. 3. The power conversion device according to claim 2, wherein when the current flowing through the bypass circuit becomes equal to or less than a predetermined value, the bypass circuit is cut off and switched to a current path through the booster circuit in which the boosting operation is stopped. The power converter according to claim 1, wherein the booster circuit is constituted by a reactor, a rectifying element, and the switch, and only the reactor is bypassed by the bypass circuit. The power converter according to claim 1, wherein the bypass circuit is configured by a relay. The power converter according to claim 1, wherein the first DC power source and the second DC power sources are connected via a DC / DC converter. The predetermined AC voltage and AC current are output and supplied to a load, or the predetermined AC output is connected in parallel to the system, and the third power source is connected to the system. The power converter device in any one of -6.

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