JPH10155280A - Inverters, power conditioners and solar power systems - Google Patents

Abstract

(57) [Problem] To provide an inverter, a power conditioner, and a photovoltaic power generation system using the same, which suppress distortion of output current to prevent generation of harmonics. A DC / DC converter (4) varies an input voltage of an inverter circuit (7), thereby limiting a duty ratio of a switching pulse of the inverter circuit (7) to a certain range in which a resonance operation of a zero voltage circuit (8) can be performed in time. The output of the inverter circuit 7, which is substantially the same as the one in which the duty ratio is not limited, is obtained to prevent the output current from being distorted because the resonance operation of the zero voltage circuit 8 cannot be made in time as in the related art. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter and a power conditioner for converting a direct current into an alternating current and a photovoltaic power generation system provided with the power conditioner.

[0002]

2. Description of the Related Art In recent years, a photovoltaic power generation system has been proposed in which a distributed power supply using a photovoltaic power generation and a commercial power supply are interconnected, and when the power cannot be provided by the distributed power supply alone, the power is supplied from the grid side. The system is being developed.

[0003] Figure 6 is a schematic configuration diagram of a photovoltaic system, reference numeral 1 denotes a solar battery as a DC power supply, 3 ₀ is not a built-in transformer, be a power conditioner of a so-called transformerless the power conditioner 3 _0, the DC / DC converter 4 of the booster type for boosting the DC voltage of the solar cell 1 at a constant voltage, the D
An inverter circuit 7 for converting DC power from the C / DC converter 4 into AC power synchronized with the system power supply 2; and switching elements S1, S2 to S2 of the DC / DC converter 4 and the inverter circuit 7. S5 is is controlled by the power conditioner controller 6 _0. L ₀ and C ₀ are a coil and a capacitor constituting the filter circuit.

The DC / DC converter 4 includes a reactor L
1, a step-up DC / DC converter including a diode D1, capacitors C1 and C2, and a switching element S1, and boosts the DC voltage of the solar cell 1 to a constant voltage of, for example, about 350V.

[0005] The inverter circuit 7 is a PWM inverter for controlling the output by changing the pulse width, and the switching elements S2 to S5 are controlled by a switching pulse based on the PWM pulse.

In the inverter circuit 7, switching noise (radiation noise) is generated because a relatively high voltage of about 350 V from the DC / DC converter 4 is switched at a high frequency of, for example, 20 kHz. There is a risk of causing trouble.

As a method of reducing such switching noise and switching loss, a so-called zero voltage switching PWM inverter which performs switching of the PWM inverter in a state where the input voltage is set to zero volt has been studied.

FIG. 7 is a configuration diagram of a system using such a zero-voltage switching PWM inverter. Parts corresponding to FIG. 6 are denoted by the same reference numerals.

[0009] In the figure, 8 is a zero voltage circuit consisting of parallel resonant DC link (Pararell Resonant DC Link) circuit, 6 ₁ zero voltage circuit 8 and the switching elements S6~S8 of the inverter circuit 7, the S2~S5 It is a power supply control unit for controlling.

The zero voltage circuit 8 includes a resonance reactor L
2. Resonant capacitors C3 and C4, diodes D2 to D
5 and switching elements S6 to S8 for temporarily reducing the input voltage of the inverter circuit 7 to 0 V by the resonance operation, so that the input voltage of the inverter circuit 7 becomes zero voltage when the inverter circuit 7 is switched. , The switching elements S6 to S8 are controlled.

[0011]

However, in such a PWM inverter using zero voltage switching, P
When the duty ratio of the switching pulse based on the WM pulse becomes, for example, about 90% or more or about 10% or less, the zero voltage circuit 8 must operate at a frequency of 10 times or more of the carrier frequency, and resonance operation is not performed. I will not be in time.

That is, FIG. 8 is a timing chart showing the input voltage of the inverter circuit 7 by the switching pulse and the zero voltage switching.
(B) shows that the duty ratio of the switching pulse is 50.
(C) and (D) show the switching pulse duty ratio of 90%, and FIGS. (E) and (F) show the switching pulse and the inverter circuit 7 when the switching pulse duty ratio is 10%. And the input voltage of each.

As shown in FIGS. 8D and 8F, when the duty ratio of the switching pulse of the inverter circuit 7 becomes about 90% or more or about 10% or less, the zero voltage circuit 8 sets the carrier frequency ( In FIG. 8, 20
kHz), the resonance operation of the zero-voltage circuit 8 cannot be performed in time, and almost no output can be obtained. Therefore, the output current is distorted and harmonics may be caused. There is a disadvantage that it becomes.

The present invention has been made in view of the above points, and provides an inverter, a power conditioner, and a photovoltaic power generation system which suppress distortion of an output current to reduce generation of harmonics. With the goal.

[0015]

In order to achieve the above-mentioned object, the present invention is configured as follows.

That is, according to the present invention, if the input voltage of the inverter circuit is varied, the same output as that obtained by varying the duty ratio can be obtained without varying the duty ratio of the switching pulse of the inverter circuit. The inverter of the present invention is an inverter circuit that converts DC from a DC power supply into an AC, and is provided between the DC power supply and the inverter circuit. When switching the inverter circuit,
A zero-voltage switching inverter including a zero-voltage circuit for setting an input voltage of the inverter circuit to a zero voltage, wherein the inverter is provided between the DC power supply and the zero-voltage circuit and varies a DC voltage from the DC power supply. And a voltage variable circuit to be applied to the zero voltage circuit.

Further, it is preferable that the voltage variable circuit varies the DC voltage so that a duty ratio of a switching pulse of the inverter circuit is within a certain range.

The inverter circuit is a PWM inverter circuit, and the zero voltage circuit is a P-type inverter circuit utilizing a resonance phenomenon.
A parallel resonant DC link circuit for reducing the input voltage of the WM inverter circuit to zero voltage, wherein the voltage variable circuit is a DC / D
It may be a C converter. The power conditioner of the present invention includes a booster circuit for boosting a DC voltage from a DC power supply, an inverter circuit for converting DC to AC, and a switching circuit for the inverter circuit provided between the booster circuit and the inverter circuit. A zero voltage circuit that sometimes makes the input voltage of the inverter circuit zero voltage, wherein the booster circuit is configured to control the DC voltage so that a duty ratio of a switching pulse of the inverter circuit is within a certain range. Is to increase the pressure.

The photovoltaic power generation system of the present invention includes a solar cell and the power conditioner of the present invention for converting DC from the solar cell into AC.

According to the inverter of the present invention, the input voltage of the inverter circuit can be varied by the voltage variable circuit. For example, the duty ratio of the switching pulse of the inverter circuit can be reduced by increasing the input voltage. On the contrary, the duty ratio can be increased by lowering the input voltage. Therefore, by varying the input voltage, the duty ratio can be kept within a certain range.

Further, according to the inverter of the present invention, by setting the certain range to a range where the resonance operation of the zero voltage circuit can be made in time, it is possible to improve the distortion of the output current and suppress the harmonics.

Further, according to the power conditioner of the present invention, the booster circuit boosts the DC voltage from the DC power supply and supplies the boosted DC voltage to the zero voltage circuit so that the duty ratio of the switching pulse of the inverter circuit is within a certain range. So
The resonance operation of the zero voltage circuit is not missed, so that the distortion of the output current can be improved and harmonics can be suppressed.

Further, according to the photovoltaic power generation system of the present invention, since the power conditioner of the present invention is provided,
Distortion of the output current at the time of a light load or a drop in input is improved, and the generation of harmonics is reduced.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a configuration diagram of a main part of a photovoltaic power generation system provided with a power conditioner according to one embodiment of the present invention, and a portion corresponding to FIG. 6 and FIG. The same reference numerals are given.

The solar power generation system according to this embodiment
A solar cell 1 as a DC power supply and a power conditioner 3 for converting DC power from the solar cell 1 into AC power synchronized with a system power supply 2 are provided. A DC / DC converter 4 as a boosting circuit for boosting a DC voltage from the battery 1, a zero voltage switching PWM inverter 5, and a power conditioner control unit 6 for controlling each unit;
As in the conventional case, a protection function for detecting a system abnormality and performing a protection operation is provided.

Zero voltage switching PWM inverter 5
Includes a PWM control type inverter circuit 7 for converting DC power to AC power, and a zero voltage circuit 8 for setting the input voltage of the inverter circuit 7 to zero voltage when the inverter circuit 7 is switched. 5
Performs switching of the inverter circuit 7, that is, so-called soft switching, in a state where the input voltage is set to zero voltage in order to reduce switching noise and switching loss.

The DC / DC converter 4 includes a reactor L1, a diode D1, and a capacitor C, as in the prior art.
, A step-up DC / DC converter including a switching element S1 and a switching element S1.
1 is controlled as described below.

The zero voltage circuit 8 includes a resonance reactor L
2. Resonant capacitors C3 and C4, diodes D2 to D
5 and a parallel resonant DC link circuit including switching elements S6 to S8, which temporarily reduces the input voltage of the inverter circuit 7 to 0 V by a resonance operation.
The switching elements S6 to S8 are controlled such that the input voltage of the switching elements S1 to S4 becomes zero.

The inverter circuit 7 is a PWM inverter for controlling the output by changing the pulse width, and the switching elements S2 to S5 are controlled by a switching pulse based on the PWM pulse.

The power conditioner control unit 6 includes a CPU
And a logic circuit, which feeds back an output voltage of the inverter circuit 7 and outputs a PWM pulse for controlling each of the switching elements S2 to S5 of the inverter circuit 7 from a sine wave and a reference triangular wave based on the feedback voltage. The switching elements S6 to S8 of the zero voltage circuit 8 are controlled so that the input voltage of the inverter circuit 7 becomes zero voltage at the time of switching of the inverter 7, and the configuration is the same as the conventional one.

In the present embodiment, it is assumed that the duty ratio of the switching pulse of the inverter circuit 7 becomes about 90% or more or about 10% or less, and the resonance operation of the zero voltage circuit 8 cannot be performed in time, so that no output can be obtained. In order to prevent this, the configuration is as follows.

That is, even if the duty ratio of the switching pulse of the inverter circuit 7 is not set to, for example, 90%, the DC / DC converter 4 allows the inverter circuit 7 to operate.
, The duty ratio is substantially 90
% Of the output of the inverter circuit 7 can be obtained. Even if the duty ratio is not 10%, for example, the inverter circuit 7 can be obtained by the DC / DC converter 4.
, The duty ratio can be substantially reduced to 10
Paying attention to the fact that the output of the same inverter circuit 7 can be obtained in%, the output voltage, that is, the input voltage of the inverter circuit 7 is varied by the DC / DC converter 4.

Conventionally, the DC / DC converter 4 boosts the voltage to a constant voltage. In this embodiment, however, the DC / DC converter 4 uses the duty ratio of the switching pulse of the inverter circuit 7. Is a certain range,
For example, the pressure is increased so as to be 20% to 80%.

That is, as shown in FIG. 2, in a portion where the duty ratio is equal to or less than 20%, the voltage is boosted to a voltage lower than the conventional constant voltage Vs. The voltage is increased to the same constant voltage Vs, and in a portion corresponding to 80% or more, the voltage is increased to a voltage higher than the conventional constant voltage Vs so that the product of the input voltage of the inverter circuit 7 and the duty ratio is always constant. By controlling the input voltage of the inverter circuit 7 in this way, the duty ratio of the switching pulse of the inverter circuit 7 is prevented from becoming less than 20% or more than 80%.

FIG. 3 is a functional block diagram of a main part of the power conditioner control section 6 for controlling the DC / DC converter 4 and the inverter circuit 7.

The reference sine wave from the CPU 9 which has been D / A converted by the D / A converter 10 and the output voltage of the inverter circuit 7 are input to the operational amplifier 11 and the error voltage thereof is amplified. The reference triangular wave from the oscillator 12 is compared by the PWM comparator 13 to control the switching elements S2 to S5 of the inverter circuit 7 based on the PWM pulse which is the comparison output, and the PWM pulse is taken into the CPU 9.

On the other hand, the CPU 9 outputs reference voltage data based on the PWM pulse so as to have the characteristics shown in FIG. 2, and the D / A converter 14 converts the reference voltage data into a digital signal. Is applied to one input of an operational amplifier 15, and the other input of the operational amplifier 15 is connected to DC / DC
The output voltage of the converter 4 is applied to amplify the error voltage, and the output of the operational amplifier 15 and the reference triangular wave from the oscillator 16 are compared by the PWM comparator 17, and the comparison output causes the switching element S1 of the DC / DC converter 4 to operate. It is controlled.

It should be noted that the present invention is not limited to the functional block diagram of FIG. 3, but may be carried out by software processing. The present invention is not limited to the voltage control type but may be a current control type. Of course.

FIG. 4 is a timing chart corresponding to FIG. 8 showing the switching pulse and the input voltage of the inverter circuit 7 by the zero voltage switching according to this embodiment. FIGS. FIG. 3C shows the switching pulse and the input voltage of the inverter circuit 7 when the duty ratio is 50%.
(D) shows the switching pulse corresponding to the conventional duty ratio of 90% and the input voltage of the inverter circuit 7, respectively, and FIGS. (E) and (F) show the conventional duty ratio of 1%.
Switching pulse equivalent to 0% and inverter circuit 7
And the input voltage of each.

As shown in FIGS. 4C and 4D, the duty ratio is 90% in the prior art, but in this embodiment, the input voltage of the inverter circuit 7 is changed by the DC / DC converter 4. 2, the duty ratio can be increased in time for the resonance operation to be sufficient.
The same output as when the duty ratio is substantially set to 90% can be obtained while limiting to 0%, and the output cannot be obtained because the resonance operation is not in time as shown in FIGS. 8 (C) and 8 (D). There is no.

As shown in FIGS. 4 (E) and 4 (F), the duty ratio is conventionally 10%, but in this embodiment, the input of the inverter circuit 7 is controlled by the DC / DC converter 4. By lowering the voltage according to the characteristics of FIG. 2, the duty ratio is substantially reduced to 10% while limiting the duty ratio to 20% at which resonance operation can be performed.
8 (E), the same output can be obtained.
There is no case where an output cannot be obtained because the resonance operation is not in time as in (F).

Since the product of the input voltage of the inverter circuit 7 and the duty ratio is always constant in the DC / DC converter 4 as described above, FIG.
The shaded areas in FIG. 8E and FIGS. 8C and 8E are equal.

FIGS. 5A and 5B show the input voltage and the output voltage of the inverter circuit 7, and FIGS. 5A and 5B show the input voltage and the output voltage of the conventional inverter circuit 7, respectively. (C) and (D) show the input voltage and the output voltage of the inverter circuit 7 of this embodiment, respectively.

Conventionally, the input voltage of the inverter circuit 7 was a constant voltage as shown in FIG. 5A, but in this embodiment, as shown in FIG. However, it is low in the period corresponding to 20% or less, and is high in the period corresponding to 80% or more. As a result, while limiting the duty ratio to 20% to 80%, FIGS. As shown, substantially the same output as the conventional example can be obtained.

As described above, by changing the input voltage of the inverter circuit 7 by the DC / DC converter 4, the duty ratio of the switching pulse of the inverter circuit 7 can be set within a certain range in which the resonance operation of the zero voltage circuit 8 can be performed. While limiting, the output is virtually the same as when the duty ratio is not limited, so that the resonance operation of the zero voltage circuit is not in time and the output cannot be obtained as in the past. Instead, this can improve the distortion of the output current and reduce the generation of harmonics.

Although the above embodiment has been described by applying the present invention to a grid-connected photovoltaic power generation system, another embodiment of the present invention relates to an independent photovoltaic power generation system independent of a grid. Of course, it may be applied.

The inverter and the power conditioner of the present invention are not limited to a solar power generation system using a solar cell as a DC power supply, but may be applied to other distributed power supply systems such as a fuel cell. It may be applied to an air conditioner system or the like.

Further, in the above-described embodiment, the duty ratio is set in the range of 20% to 80%, but it is needless to say that the duty ratio is not limited to this range.

[0050]

As described above, according to the present invention, DC / D
Since the input voltage of the inverter circuit can be varied by varying the DC voltage by a voltage variable circuit such as a C converter, the duty ratio of the switching pulse of the inverter circuit can be reduced by using a zero voltage circuit such as a parallel resonant DC link circuit. It is possible to obtain the same output that does not substantially limit the duty ratio while limiting to a certain range in which the resonance operation can be performed in time. It is no longer possible to obtain the output current, thereby improving the distortion of the output current and reducing the generation of harmonics.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a photovoltaic power generation system according to one embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of the DC / DC converter of FIG.

FIG. 3 is a functional block diagram of a main part of a power conditioner control unit of FIG. 1;

FIG. 4 is a timing chart of a switching pulse and an input voltage of an inverter circuit of FIG. 1;

FIG. 5 is a diagram showing an input voltage and an output voltage of the inverter circuit.

FIG. 6 is a configuration diagram of a conventional solar power generation system.

FIG. 7 is a configuration diagram of a system using a zero voltage switching PWM inverter.

FIG. 8 is a timing chart of a switching pulse and an input voltage of an inverter circuit of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Solar cell 3,3 ₀ Power conditioner 4 DC / DC converter 5 Zero voltage switching PW
M inverter 7 Inverter circuit 8 Zero voltage circuit 6,6 ₀ Power conditioner controller

Claims (5)

[Claims] An inverter circuit for converting a direct current from a direct current power supply into an alternating current, and an input voltage of the inverter circuit being reduced to zero voltage when the inverter circuit is switched between the direct current power supply and the inverter circuit. A zero-voltage switching inverter, comprising: a zero-voltage switching inverter provided between the DC power supply and the zero-voltage circuit, the DC voltage from the DC power supply being variable and applied to the zero-voltage circuit. An inverter comprising a circuit. 2. The voltage variable circuit varies the DC voltage such that a duty ratio of a switching pulse of the inverter circuit is within a certain range.
Inverter as described. 3. The inverter circuit is a PWM inverter circuit, and the zero voltage circuit is a parallel resonant DC link circuit that makes an input voltage of the PWM inverter circuit zero voltage using a resonance phenomenon, and the voltage variable. The circuit is D
3. The inverter according to claim 1, wherein the inverter is a C / DC converter. 4. A booster circuit for boosting a DC voltage from a DC power supply, an inverter circuit for converting DC to AC, and the inverter provided between the booster circuit and the inverter circuit when the inverter circuit is switched. A booster circuit that boosts the DC voltage so that a duty ratio of a switching pulse of the inverter circuit is within a certain range. A power conditioner characterized by the following. 5. A photovoltaic power generation system comprising: a solar cell; and the power conditioner according to claim 4, which converts a direct current from the solar cell into an alternating current.