JP2000324852A - Current type inverter for photovoltaic power generation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current type inverter for photovoltaic power generation having low loss and high conversion efficiency in which the number of electronic parts passing a high frequency current is decreased while reducing noise. SOLUTION: The current type inverter 10 for photovoltaic power generation comprises a bridge type switching circuit 36 comprising four semiconductor switching elements 28-34 connected, respectively, in series with diodes 20-26 receiving DC power from a solar cell array section 12 through a reactor 18, and a current type inverter section 14 having a PWM control circuit 38 outputting a switching control signal to each semiconductor switching element 28-34 wherein DC power is converted into AC power through the current type inverter section 14 and linked with a commercial power system. The reactor 18 is divided uniformly into two and arranged symmetrically to the solar cell array section 12 and a high frequency semiconductor switching element 40 is connected to the input side of the switching circuit 36 in parallel therewith.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current-source inverter device for photovoltaic power generation, and more particularly to a current-source inverter device for photovoltaic power generation, for example, converting DC power of a solar cell into AC power and interconnecting with a commercial power system. .

[0002]

2. Description of the Related Art In recent years, attention has been paid to clean energy free of environmental pollution, especially solar power generation using a solar cell, due to increasing awareness of global environmental protection, and practical use thereof has been promoted. In this photovoltaic power generation, the generated power fluctuates greatly in accordance with the amount of solar radiation, so in order to ensure a stable supply of power and effective use of surplus generated power, the solar power consisting of solar cells and inverters installed in buildings and ordinary households The power generation system is used in connection with a commercial power system. That is, power is normally supplied to a load, for example, an inverter air conditioner, by parallel operation of the solar power generation system and the commercial power system. Then, part or all of the electric power required for the house is covered by the solar power generation, and when the power generated by the solar cell is excessive, a reverse power flow is supplied to the commercial power system.

In general, DC power is converted into single-phase AC power by, for example, as shown in FIG. 8, four semiconductor devices which are switching devices having a self-turn-off function, for example, a high-speed semiconductor switching device (IGBT). Q1
A single-phase bridge voltage-source inverter main circuit including Q4 and four feedback diodes D1 to D4 connected in anti-parallel to these switching elements is used.

In this inverter main circuit, a set of semiconductor switching elements Q1 and Q4 and a set of semiconductor switching elements Q2 and Q3 are divided, and each set is alternately switched (open / closed), so that the semiconductor switching element Q
1, the connection point of Q2 and the semiconductor switching elements Q3, Q4
A staircase-like voltage is obtained between the connection point and the connection point. And
Pulse width modulation (PWM) suitable for switching control signals
, The output voltage waveform can be approximated to a sine waveform. That is, the inverter main circuit that converts DC power and outputs single-phase AC power includes a switching circuit and a PWM control circuit that controls the operation of this circuit.

In principle, the input DC voltage of the inverter main circuit may be a peak value (about 1.4 times the effective value) of the output AC voltage. However, in practice, the semiconductor switching elements Q1 to Q4 The voltage is set to about twice the output AC voltage (effective value) in consideration of the voltage drop of the filter circuit, the voltage drop of the filter circuit, and the temperature characteristics of the DC power supply (solar cell).

[0006]

However, an inverter that converts direct current to alternating current has a problem that a large amount of noise is generated due to fluctuations in the voltage between the input and output of the inverter.

That is, in the inverter main circuit,
The intensity of the high-frequency voltage between the ground of the power line has a great influence on the amount of noise emission. Usually, noise is observed as "the magnitude of the high-frequency voltage with respect to the ground". That is, in FIG. 9, if the input / output terminals of the inverter main circuit 3 arranged between the solar cell array unit 1 and the commercial AC power supply 2 are P, N, U and V, the N terminal and the ground and the V terminal The high-frequency components of the voltages VNE and VVE between the grounds correspond to “the magnitude of the high-frequency voltage with respect to the ground”. In addition, each voltage between P terminal and ground and between U terminal and ground
VPE and VUE are defined similarly.

When the inverter operates, it is necessary to pay attention to the movement of the input / output voltage as described above. In particular, in a system in which a transformer is not used internally, since the input / output terminals are connected through the switching elements constituting the inverter main circuit 3, the voltage between the input and output sharply changes and VN
In order to change E and VVE, this may significantly increase the amount of noise radiation. Also, the change in voltage with respect to ground is commonly referred to as "common mode voltage".

The voltage between each terminal (PN, UV) on the DC and AC sides of the inverter main circuit 3 is a DC voltage
It is an AC voltage and has a fixed value. Since the AC side is a system voltage, the instantaneous value is alternating current but has a very low frequency, so that the influence as noise can be ignored.

In the conventional current source inverter as shown in FIG. 10, a very large amount of noise is generated as described above. This is due to the switching method and the operation of the inverter main circuit.

That is, in the case of a single-phase three-wire 200 V on the system side, the neutral phase O-phase is grounded by a pole transformer. Therefore, it is considered based on this. O phase is always U
It is the midpoint of the voltage between -V. FIG. 11 shows a timing chart based on a commonly used waveform generation pattern.

For example, when a current flows in the direction of "U → V", the switching elements Q1 and Q4 in FIG. 10 are always turned on, and PWM is generated so that the OFF time becomes longer as a larger current flows through Q2. Then, the input current Ii
n flows to the output side in accordance with the PWM ratio. As a result, the longer the OFF time of Q2, the larger the output current. Conversely, when a current flows in the direction of “V → U”, Q
2. The current amount can be controlled by always turning on Q3 and controlling Q4 by PWM.

Referring to the switching elements (Q1 to Q4), when each element is turned on and off, a voltage determined by a peripheral circuit is applied when the element is turned off. In the case of a current-source inverter, this is about the voltage normally handled.
In the case of the interconnection operation with respect to V, 282 V which is the maximum value of 200 V AC is the maximum. Conversely, both ends of the switching element are ON voltage when ON, and have a very small value (about 1 to 2 V) as compared with OFF. As a result, the situation of each switching ON-OFF cycle can be analyzed.

Therefore, the voltage on the output side is 2
Assume 00V (100V on one side) and 50V on the input side.

In FIG. 10, Q of the switching element
When 1, Q2, Q4 = ON and Q3 = OFF, the input / output voltage is as shown in FIG. In the figure, both the switching element and the diode which are ON are omitted. In this case, 50 V DC is applied to the input reactor, and the input current Iin increases. Also, the output current Iout
Is supplied from the output side capacitor Cout and decreases. When the AC side O-phase is used as a reference, the P-phase becomes 150 V and the N-phase becomes 100 V, as is apparent from the figure.

Next, FIG. 13 shows a circuit diagram when Q2 = OFF from FIG. Since Q2 = OFF, the output side capacitor Co is generated by the input current Iin.
ut is charged, and the insufficient voltage for charging is supplemented by the input reactor. Although the diode D4 is OFF in FIG. 11 due to the reverse bias, the switching element Q2
Since the FF has been turned on, the OFF voltage of Q2 supports the voltage on the output side, and is turned ON to allow the return current of the input current Iin to flow. Also in this case, when considering the AC side O-phase as a reference, the N-phase is -100 V and the P-phase is -50 V, which is 50 V higher than the N-phase.
Becomes

In the next half cycle, the relationship of the AC voltage becomes V> U. FIG. 14 shows a circuit diagram when Q1 = OFF and Q2, Q3, Q4 = ON. Q2 = ON, but since V> U, diode D2 is reverse biased and OFF.
Considering the O phase as a reference, the P phase is 150 V, the N phase is 10 V
0V.

Finally, Q1, Q4 = OFF, Q2, Q3 =
FIG. 15 shows a circuit diagram in the case of ON. In this circuit diagram, since it can be considered that U and V are interchanged in FIG. 13, when the O phase is used as a reference, the P phase is −50 V, and the N phase is −50 V.
100V.

The waveform generation pattern shown in FIG.
The results obtained in FIG. 15 are summarized as follows.

1) When U> V, the switching O of Q2
The potential seen from the O phase in N-OFF is as follows.

P phase 150V → −50V → 150V → −50V →... ± 100V N phase 100V → −100V → 100V → −100V →... ± 100V 2) When U <V, V phase when switching ON / OFF of Q4 The potential as seen from is as follows.

P-phase 150V → −50V → 150V → −50V →... ± 100V N-phase 100V → −100V → 100V → −100V →... ± 100V A swing of ± 100V occurs in any cycle. This is a change in voltage generated by each switching. Since the switching frequency is usually set to a value higher than the audio frequency, a frequency of 15 to 17 kHz or more is often used. Therefore, for the P and N phases, the upper voltage change is 15
It occurs in the range of ~ 17 kHz.

On the other hand, since the system voltage is AC, voltage changes occur at U and V shown in FIGS. 12 to 15 at commercial frequencies (50 and 60 Hz). Generally, neutral phase (0 phase) of system voltage
Is grounded, so that the voltage changes 1) and 2) used in the above verification are generated with respect to the ground, and the magnitude of the high-frequency component (150 kHz or more) becomes noise and is observed. Is done. 150k according to VCCI
At 79 Hz, it is 79 dBV or less, which corresponds to 89 mV or less at the voltage level. 10th harmonic (15
Considering that it is 89 mV or less at 0 kHz), 1
It can be seen that a voltage change of ± 100 V at 5 kHz is a very large noise level.

SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide a current source inverter for photovoltaic power generation which has a simple structure, reduces noise generation, and has high conversion efficiency.

[0025]

SUMMARY OF THE INVENTION The present invention provides a bridge-type switching circuit which receives DC power from a solar cell via a reactor and includes four semiconductor switching elements, and supplies a switching control signal to each semiconductor switching element. A current-source inverter unit having a pulse width modulation control circuit for outputting the current-source inverter unit. The current-source inverter unit converts the DC power of the solar cell into AC power and interconnects with a commercial power system. And a high-frequency switching unit provided in parallel with the switching circuit on the output side of the reactor.

Further, according to the present invention, in the above-described current-source inverter for photovoltaic power generation, the reactor is equally divided into two parts, symmetrically arranged and connected to the solar cell, and the switching circuit is connected to the input side of the switching circuit. A current source inverter for photovoltaic power generation, wherein a high-frequency switching unit is provided in parallel.

[0027]

Since the high-frequency switching section is provided in parallel with the switching circuit on the output side of the reactor, the high-frequency portion flows by bypassing another route during the operation of the switching circuit, and the number of electronic components through which the current passes can be reduced. Further, since the reactor is equally divided into two and arranged symmetrically on the input side, the potential does not change during switching, and generation of noise is suppressed.

[0028]

According to the present invention, since the conversion efficiency is improved and the noise is reduced, it is possible to provide a small-sized and high-performance current-source inverter for photovoltaic power generation at low cost.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the accompanying drawings.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A current source inverter device 10 for photovoltaic power generation according to an embodiment of the present invention shown in FIGS.

In FIG. 1, a current-source inverter device 10 for photovoltaic power generation includes a current-source inverter unit 14 that receives DC power from a solar cell array unit 12 and an output filter circuit 16.

The solar cell array section 12 comprises the same number of reverse current blocking diodes as a plurality of solar cells (not shown). The required number of solar cells and reverse current blocking diodes are connected in series or as many as necessary according to the output capacity. Connected in parallel.

The current source inverter unit 14 converts the DC power generated by the solar cell array unit 12 into AC power, and includes a current smoothing reactor 18 for smoothing high-frequency ripples and diodes 20, 22, 24, Semiconductor switching elements 2 each of which is connected in series with
8, 30, 32, and 34 connected in a bridge form, and a pulse width modulation control circuit (P) that outputs a switching control signal to each of the semiconductor switching elements 28 to 34 of the switching circuit 36.
WM control circuit) 38. This PWM control circuit 38
Is a feedback control system that detects the output current of the switching circuit 36 with a current detector (not shown) and feeds back the switching current, and switches a plurality of sets of PWM pulses whose pulse widths are adjusted so that the output state of the switching circuit 36 becomes appropriate. This is supplied to each of the semiconductor switching elements 28 to 34 constituting the circuit 36.

Further, a high frequency semiconductor switching element 40 is connected in parallel with the switching circuit 36 on the output side of the current smoothing reactor 18. As a result, for example, when the semiconductor switching elements 28 and 30 are simultaneously turned on, the high-frequency semiconductor switching element 40 is turned on so that the high-frequency current flows toward this element 40. Thereby, the conventional semiconductor switching elements 28 and 3
A loss corresponding to 0 and four of the diodes 20 and 22 is only the switching element 40.

Therefore, by separating the high-frequency switching portion from the switching circuit 36, the flow of the high-frequency current changes, the number of devices through which this current passes is reduced, and the conversion efficiency is improved by about 0.5 to 1%. That is, in the conventional example shown in FIG. 10, when switching as shown in FIG. 11 is performed, high-frequency switching is performed by the switching elements Q2 and Q4. However, during the switching cycle, the switching elements Q1, Q2 or Q3. There is a time when Q4 is simultaneously ON. At this time, the current (Iin) includes two switching elements and a diode 2
Pass through the pieces. The resulting loss is a value that cannot be ignored. Further, as described above, in this current source inverter main circuit system, the current always flows through the switching element 2.
And two diodes.
This is a loss for each item. To explain this in detail, for example, in the case of an inverter having an input current of 30 A and an output current of 15 A, the current flowing through this circuit is not the output 15 A but the input 30 A. Therefore, when the ON voltage of the switching element and the diode is 3 V in total, 30 A ×
A loss of 3V × current passing time occurs. This loss is
Usually, it is a large value that cannot be ignored.

The output filter circuit 16 includes a capacitor 42 connected to the output terminal of the switching circuit 36, and reactors 44, 44, and has an inverted L-shape for obtaining an output with a low frequency component. A load and a commercial power system (not shown) are interconnected to the output filter circuit 16.

Next, an outline of the operation of the current-source inverter device 10 for photovoltaic power generation in the above configuration will be described.

First, the electromotive force generated in the solar cell array unit 12 by the irradiation of sunlight smoothes the high-frequency ripple by the current-smoothing reactor 18, causes the high-frequency component to flow to the high-frequency semiconductor switching element 40, and switches the smooth portion. The signal is input to the circuit 36. This switching circuit 36
Then, a plurality of sets of PWM pulses whose pulse widths are adjusted by the PWM control circuit 38 so that the output state becomes appropriate are supplied as switching signals to the semiconductor switching elements 28 to 34 constituting the switching circuit 36. as a result,
An alternating current with less distortion is output from the switching circuit 36, and the output filter circuit 16 further removes high-frequency components, and is connected to a load or a commercial power system.

In this embodiment, only the high-frequency semiconductor switching element 40 (Q5) is subjected to high-frequency switching (15 kHz), so that the other four semiconductor switching elements 28 to 34 ( Q1 to Q4) may be switched at the frequency of the output current. A switching pattern indicating the timing at that time is shown in FIG. As is apparent from this figure, only the high-frequency semiconductor switching element 40 (Q5) performs high-frequency switching by comparing PWM generation triangular waves. When the element 40 (Q5) is ON, the output side semiconductor switching elements 28 to 34 (Q1 to Q4)
Although it is N, there is no problem in operation since the diodes 20 to 26 prevent backflow. Since the output-side semiconductor switching elements 28 to 34 (Q1 to Q4) switch at the commercial frequency as described above, those having a lower switching speed than the high-frequency switching element 40 (Q5) can be used. For example, a bipolar transistor or the like has a low speed but a low voltage at ON, a low loss, and a low price.

Next, another embodiment shown in FIG. 2 will be described. The same components as those in the embodiment of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

In another embodiment, a bridge-type switching circuit 3 constituting a current-source inverter main circuit is used.
The four diodes 20 to 26 (see FIG. 1) connected in series to the respective semiconductor switching elements 28 to 34 constituting 6 are moved as one common diode 46 to a stage preceding the switching circuit 36 and connected thereto. I have. Therefore, when the high-frequency semiconductor switching element 40 is ON, it is separated from the output side by the common diode 46, so that only one diode is sufficient. As a result, the loss can be further reduced as compared with the embodiment shown in FIG.

The third embodiment shown in FIG. 3 is a further improvement of the embodiment shown in FIG. 2, and the same components are denoted by the same reference numerals and description thereof is omitted.

In the third embodiment, the output filter circuit 16 (including the reactor 42 and the capacitor 42 for removing high-frequency components connected to the output terminal side of the switching circuit 36 constituting the current source inverter main circuit). 2 is disposed as a filter circuit 48 in a stage preceding the switching circuit 36. That is, the capacitor 42 constituting the filter circuit 48 is connected in parallel to the switching circuit 36, and the reactor 44 is connected in series. Since the high frequency component is removed by the filter circuit 48, no high frequency current flows through each of the semiconductor switching elements 28 to 34 constituting the switching circuit 36. Therefore, the loss is further reduced as compared with the embodiment shown in FIG.

Further, the fourth embodiment according to the present invention shown in FIG. 4 reduces the occurrence of noise due to the fluctuation of the input / output voltage of the current source inverter main circuit. The current smoothing reactor 18 is divided equally into two reactors 18a and 18b.
8a and 18b are symmetrically arranged and connected so as to form a pair on the input side. The same components as those in the embodiment of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. By devising the circuit configuration on the input side in this manner, high-frequency fluctuations of the ground voltage are suppressed, and low noise is enabled.

Next, an outline of the operation of the fourth embodiment will be considered. First, in FIG. 4, the high-frequency semiconductor switching element 40 and the semiconductor switching element 2
FIG. 5 shows a circuit configuration in the case where both 8 and 34 are ON and the semiconductor switching elements 30 and 32 are both OFF. Here, the voltage on the output side is 200 V as an instantaneous value of AC.
(100 V on one side) and 50 V on the input side.
As is apparent from this figure, the diodes 20 and 26 are
As F, the reactors 18a and 18b are apparently separated. At this time, the reverse voltages supported by the diodes 20 and 26 are not always equal, but this indicates that the reverse voltage depends on the immediately preceding value.

Thus, the P and N phases become the O phase and the target potential. That is, in FIG. 5, the P phase is +25 V, and the N phase is -2.
5V. In the next cycle, the high-frequency semiconductor switching element 40 is turned off. FIG. 6 shows the circuit configuration at this time. Since the reactors 18a and 18b equally share the difference with the system voltage, the potentials of the P and N terminals are symmetrically arranged with respect to the O phase, and the P phase is +2 from the O phase.
The 5 V and N phases have a potential of −25 V from the O phase.

In FIG. 5, since the potentials of the P and N terminals are not directly related to the O phase due to the reverse voltage generated by the diodes 20 and 26, the cycles of FIGS. 5 and 6 occur alternately. Can be considered to have inherited the state of FIG.

Similarly, the semiconductor switching element 28
And 34 are OFF, and the semiconductor switching elements 30 and 32 are ON. However, this is because the relationship between U and V is reversed in FIGS. 5 and 6 and the potentials of P and N do not change. Omitted.

As described above, in all the switching operations in the fourth embodiment shown in FIG. 4, the potentials of P and N do not change, and as a result, generation of noise is suppressed. That is, when the countermeasure according to the present invention is applied to the input side of the current source inverter main circuit, noise of 130 dBμV is 9%.
It has been reduced to 0 dBμV. In the embodiment of FIG. 4, if a smoothing capacitor is additionally connected in parallel with the solar cell array unit 12, the effect of reducing noise is further increased.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a schematic configuration of a current source inverter device for photovoltaic power generation according to an embodiment of the present invention.

FIG. 2 is a main part circuit diagram of another embodiment according to the present invention.

FIG. 3 is a main part circuit diagram of a third embodiment according to the present invention.

FIG. 4 is a main part circuit diagram of a fourth embodiment according to the present invention.

FIG. 5 is a circuit diagram in a certain operation in FIG. 4;

FIG. 6 is a circuit diagram showing another operation in FIG. 4;

FIG. 7 is a timing chart of a switching pattern in the embodiment shown in FIG. 1;

FIG. 8 is a circuit diagram of a conventional voltage source inverter device.

FIG. 9 is a block diagram for explaining an outline of noise generation when an inverter main circuit is provided between a solar cell array unit and a commercial AC power supply.

FIG. 10 is a circuit diagram of a conventional current source inverter device.

FIG. 11 is a timing chart of switching based on a commonly used waveform generation pattern.

FIG. 12 is a diagram showing switching elements Q1, Q
2 is a circuit diagram when Q4 is ON and Q3 is OFF.

FIG. 13 shows switching elements Q1, Q
FIG. 4 is a circuit diagram in a case where 4 is ON and Q2 and Q3 are OFF.

FIG. 14 is a diagram showing the switching element Q1 being OFF and the switching elements Q2, Q3 and Q4 being ON when the AC voltage relationship is V> U.
FIG. 9 is a circuit diagram in the case of FIG.

FIG. 15 shows switching elements Q1, Q in FIG.
FIG. 4 is a circuit diagram in a case where 4 is OFF and Q2 and Q3 are ON.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Current-source inverter apparatus for photovoltaic power generation 12 ... Solar cell array part 14 ... Current-source inverter part 16 ... Output filter circuit 18 ... Current smoothing reactor (input reactor) 20-26 ... Diode (D1-D4) 28-34 ... Semiconductor switching elements (Q1 to Q4) 36 ... Switching circuit 38 ... Pulse width modulation control circuit (PWM control circuit) 40 ... Semiconductor switching element for high frequency (Q5) 42 ... Capacitor 44 ... Reactor 46 ... Common diode 48 ... Filter circuit

Claims (6)

[Claims] 1. A bridge-type switching circuit that receives DC power from a solar cell via a reactor and includes four semiconductor switching elements, and a pulse width modulation control circuit that outputs a switching control signal to each of the semiconductor switching elements. A current source inverter section having
In the current source inverter device for photovoltaic power generation, which converts the DC power into AC power by the current source inverter unit and interconnects with a commercial power system, high-frequency switching is performed in parallel with the switching circuit on the output side of the reactor. A current source inverter device for photovoltaic power generation, characterized by having an inverter unit. 2. The current source inverter for photovoltaic power generation according to claim 1, wherein said high frequency switching section includes a high frequency semiconductor switching element. 3. The current-source inverter for photovoltaic power generation according to claim 1, wherein a common diode is further connected in series before the switching circuit. 4. The current source inverter for photovoltaic power generation according to claim 1, further comprising an output filter circuit formed of a capacitor and a reactor connected to an output terminal of said switching circuit. 5. The current source inverter for photovoltaic power generation according to claim 3, wherein a filter circuit formed by a capacitor and a reactor is connected between said common diode and said switching circuit. 6. The reactor, wherein the reactor is equally divided into two and symmetrically arranged and connected to the solar cell.
A current-source inverter device for photovoltaic power generation according to claim 1.