JPH0954623A - Linkage type power converting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linkage type power converting device which is small in size and light in weight and can effectively make good use of the maximum output electric power of a solar battery and protect a load connected to a system power distribution line against an overvoltage. SOLUTION: This device is equipped with a DC-DC converting circuit 3 which inputs the DC output of the solar battery 100 and performs DC-DC conversion, a DC-AC converting circuit 4 which inputs the output of the DC-DC converting circuit and performs DC-AC conversion, and a control circuit 6, which computes the electric power of the DC output of the solar battery and controls the input impedance of the DC-DC converting circuit. Consequently, the maximum output of the solar battery 100 is inputted to the DC-DC converting circuit 3 and effectively used. Further, the device is reduced in size and made light in weight by using a high-frequency insulating transformer. Further, an overvoltage of the system power distribution line is detected and the operation of the device is stopped to protect the load connected to the system power distribution line against the overvoltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interconnection type power conversion apparatus for converting a DC output of a solar cell into an AC power in a photovoltaic power generation system installed in a house, and for causing a reverse flow in a system distribution line.

[0002]

2. Description of the Related Art Conventionally, in a photovoltaic power generation system, when DC power generated by a solar cell is supplied to a system distribution line, the DC power of the solar cell is supplied to a system distribution line side by a connection type power conversion circuit. The power is converted into frequency-coordinated power and supplied.

FIG. 10 shows a conventional interconnection type power conversion device 10.
It is a system block diagram showing the photovoltaic power generation system to which 1 was applied. Output electrodes (+ and-) of solar cell 100
P and N are connected to the input of the interconnection type power converter 101, and the output of the interconnection type power converter 101 is the interconnection protection device 1.
It is connected to the system distribution line 106 fed from the system power supply 103 via 02. The interconnection protection device 102 is installed for the purpose of performing protection cooperation between the interconnection power conversion device 101 and the system distribution line 106, and there is also a device incorporated in the interconnection power conversion device 101. .

Here, the conventional interconnection type power converter 101
Is a DC-AC conversion circuit 104 that converts DC power generated by the solar cell 100 into AC power, and commercial insulation that transforms the AC output of the DC-AC conversion circuit 104 to prevent contact with the system distribution line. It is composed of a transformer 105. This commercial isolation transformer 105 is a large heavy object,
The DC-AC conversion circuit 104 is incorporated in the interconnection type power conversion device 101 independently of the DC-AC conversion circuit 104. Interconnected power converter 10
The AC power obtained by converting by 1 is the interconnection protection device 1
The power is supplied to the system distribution line 106, which is fed from the system power supply 103, through the reverse power flow.

Further, as disclosed in Japanese Patent Application Laid-Open No. 2-81107, a high-frequency insulation transformer T ₂ is used in place of the large-sized heavy duty commercial insulation transformer 105, so that the apparatus is small and lightweight. It is known that it has been made into a product.
FIG. 11 is a system block diagram in which the interconnection type power conversion device 111 configured by using the high frequency insulation transformer T ₂ is applied to a solar power generation system. This interconnection type power conversion device 111 converts the DC output of the solar cell 100 into a voltage by a DC-DC converter 112 and further converts it into AC power by a DC-AC converter 113, and then the grid distribution line 106.
It is converted into electric power in cooperation with the side voltage and frequency and output.

[0006]

By the way, there is a problem that it is difficult to reduce the size and weight of the conventional interconnection type power conversion device 101 using the large-sized and heavy commercial insulation transformer as described above. It was

On the other hand, Japanese Patent Laid-Open No. 2-8110
Interconnected power converter 111 disclosed in Japanese Patent Publication No.
Is effective in reducing the size and weight of the device, but the solar cell 1
Since the output voltage of 00 is constant, the maximum output power of the solar cell 100 that fluctuates depending on the intensity of received sunlight or the temperature of the solar cell element cannot be extracted, and the power generated by the solar cell 100 can be effectively used. There was a problem that I could not.

Further, the interconnection protection device 102 is indispensable for protection cooperation during interconnection operation with the system distribution line 106, which also hinders downsizing and cost reduction of the device.

Further, for example, when a single-phase two-wire type 200V output interconnection type power converter is connected to the 200V side of a single-phase three-wire type 200V / 100V distribution line, the interconnection type power converter and grid distribution line When a switch (for example, an earth leakage breaker of a switchboard) connected between and is released, a single-phase three-wire type 200
For the load connected to the 100V side of the V / 100V distribution line,
An overvoltage may be applied by electric power from the interconnection type power converter side. To protect the load from this overvoltage,
It was necessary to provide an overvoltage protection relay at the output of the interconnected power converter.

The present invention has been made in view of the above problems, and it is possible to configure the device in a small size and a light weight, to effectively use the maximum output power of the solar cell, and to further improve the system distribution. An object of the present invention is to provide an interconnection type power conversion device capable of protecting a load connected to an electric wire from overvoltage.

[0011]

In order to solve the above-mentioned problems, the present invention has the following arrangement.

According to a first aspect of the present invention, there is provided an interconnection type power conversion device in which a DC-DC conversion circuit for inputting a DC output of a solar cell to perform DC-DC conversion and an output of the DC-DC conversion circuit are input. And a DC-AC conversion circuit for performing DC-AC conversion, and a control circuit, the control circuit calculates the power of the DC output of the solar cell, and the input of the DC-DC conversion circuit based on the calculation result. It is configured to control impedance.

According to a second aspect of the present invention, there is provided a grid-type power conversion device in which the DC-DC conversion circuit of the grid-type power conversion device according to the first aspect of the invention receives the output of the solar cell as a high frequency signal. A switching circuit for converting to electric power and outputting the electric power; a high-frequency insulating transformer for inputting the output of the switching circuit; and a rectifying circuit for rectifying the output of the high-frequency insulating transformer. Is controlled so that the input impedance thereof is controlled by the control circuit.

According to a third aspect of the present invention, there is provided an interconnection type power conversion device in which the control circuit of the interconnection type power conversion device according to the first aspect of the present invention has a solar cell output power of a DC-DC conversion circuit. When the input exceeds the allowable input, the input of the DC-DC converting circuit is configured to control the input impedance of the DC-DC converting circuit within a range not exceeding the allowable input current and the allowable input power of the DC-DC converting circuit. .

According to a fourth aspect of the present invention, there is provided an interconnection type power conversion device in which the control circuit of the interconnection type power conversion device according to the first aspect of the present invention has a voltage of a grid distribution line with respect to a neutral line or a frequency thereof. And a control circuit configured to temporarily stop the operation of one or more element circuits that control the operation of the control circuit, based on the result detected by the detection means. There is.

According to the interconnected power converter of the first aspect of the invention, the output voltage of the solar cell changes if the input impedance of the DC-DC conversion circuit, which is an output load when viewed from the solar cell side, changes. However, the output power of the solar cell changes along its characteristic curve. The control unit calculates the output power of the solar cell and controls the input impedance of the DC-DC conversion circuit so that the output of the solar cell becomes the maximum power.

According to the interconnection type power converter of the second aspect of the present invention, the amount of current flowing through the switching circuit is controlled by controlling the conduction time of the switching circuit which is the output load of the solar cell. . As a result, DC-
The input impedance (load characteristic of the solar cell) of the DC conversion circuit is controlled.

According to the interconnection type power converter of the third aspect of the present invention, the control circuit controls the DC-DC converter circuit when the output power of the solar cell exceeds the allowable input of the DC-DC converter circuit. The input impedance of the DC-DC conversion circuit is increased within a range in which the input does not exceed the allowable input current and the allowable input power of the DC-DC conversion circuit. As a result, the output point of the solar cell deviates from the high output area including the maximum output point,
The power input to the DC-DC conversion circuit is limited.

According to the interconnection type power converter of the fourth aspect of the present invention, the control circuit detects the voltage of the system distribution line or its frequency, and temporarily stops the operation of the DC-DC converter circuit or the like. Then, the interconnection type power conversion device is protected.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system block diagram showing a configuration of a photovoltaic power generation system provided with an interconnected power converter 1 according to an embodiment.

The interconnected power converter 1 is a solar cell 100.
The DC output generated by the converter is converted into AC power of 200V (V _ug ) single-phase two-wire system, and the output is single-phase three-wire system 200V / 1.
The system is connected to 200V of the 00V system distribution line 11 to perform interconnection operation.

Electric power supplied from the system power source 103 is supplied to the single-phase three-wire system distribution line 11 by the pole transformer 10.
Power is supplied after being transformed into 00V and 200V. That is, the neutral point terminal N of the pole transformer 10 is grounded, and 100 V (V ₁ ) is output between the neutral point terminal N and the output terminal H. Further, 100 V (V ₂ ) is output between the neutral point terminal N and the output terminal L, and 200 V (V _ug ) is output between the terminal H and the output terminal L. .

Further, the output terminal A of the interconnection type power converter 1
_{Between OUT} and B _OUT , 200 V (V _ug ) appears as the output of the interconnection type power converter 1, and these output terminals A
_OUT and B _OUT are pole transformers 10 via a grid 11
Is connected to terminals H and L which are 200 V output terminals.

The structure of the interconnection type power converter 1 incorporated in the solar power generation system in this way will be described below. The interconnection type power conversion device 1 includes a main circuit (without reference numeral) configured by each element circuit of an input relay 2, a DC-DC conversion circuit 3, a DC-AC conversion circuit 4, and an interconnection relay 5, and this main circuit. The control circuit 6 for controlling and the current sensors 8 and 9 for detecting the input current I _in of the DC-DC conversion circuit 3 and the output current I _out of the DC-AC conversion circuit 4, respectively.
And a control power supply 7 that inputs a part of the electric power output from the solar cell to generate the operating electric power of the control circuit 6.

The structure will be described in more detail below. First, the input terminals 2a and 2b of the input relay 2 are connected to the pair of input terminals A _IN and B _IN to which the output of the solar cell 100 is connected, and the output terminals 2c and 2d of this relay 2 are connected to the connection point A ₀ ,
It is connected to the input of the DC / DC converter 3 via B ₀ .
Further, the input of the control power supply 7 is connected to the input terminals A _IN and B _IN , and the output of the control power supply 7 is given to the control circuit 6 as its operating power supply. On the other hand, the DC-DC conversion circuit 3
Is connected to the input of the DC-AC conversion circuit 4 via the connection points A ₁ and B ₁ , and the output of the DC-AC conversion circuit 4 is connected to the interconnection relay 5 via the connection points A ₂ and B ₂ . Input terminal 5
a, 5b. The output terminals 5c and 5d of the interconnection relay 5 are respectively connected to the terminals A _OUT and B _OUT which are the output terminals of the interconnection type power converter 1.

Between the input terminal A _IN and the terminal 2a of the input relay 2, a current sensor 8 for detecting the current I _in input to the DC-DC conversion circuit 3 is provided, and the DC sensor Between the output of the AC conversion circuit 4 (on the side of the connection point A ₂ ) and the input terminal 5a of the interconnection relay 5, a current sensor 9 for detecting the current I _out output from the DC-AC conversion circuit 4. Is provided.

The currents I _in and I _out detected by the current sensors 8 and 9 are given to the control circuit 6 as information. Further, the control circuit 6 includes a voltage V _in input from the solar cell 100 to the DC / DC conversion circuit 3, an output voltage V _{C of} the DC / DC conversion circuit 3, an output voltage V _{out of the} DC / AC conversion circuit 4, and The voltages V ₁ , V ₂ , and V _{ug of the} single-phase three-wire system distribution line 11 to which the output terminals A _OUT and B _{OUT of the} interconnection type power converter 1 are connected are given as information. And
Based on these pieces of information, the control circuit 6 gives the relay control signals SR ₁ and SR ₂ to the input relay 2 and the interconnection relay 5, respectively, and outputs the drive signals SC ₁ and SC ₂ to the DC-DC conversion circuit 3 and DC, respectively. -It is given to the AC conversion circuit 4.

Here, the control circuit 6 has the following 5 described below.
Has two control functions. That is, first, the input relay 2
, The second, the input impedance control function of the DC-DC conversion circuit 3, the third, the output current I _out control of the DC-AC conversion circuit 4, the fourth, the disconnection control function of the interconnection relay 5, Fifth, it has a function of detecting an abnormality in the voltage or frequency of the system distribution line and stopping the power conversion operation of the interconnection type power conversion circuit 1. Details of these functions and the circuit configuration for achieving them will be described later in the description of the operation.

FIG. 2 is a circuit diagram showing the configuration of the DC-DC conversion circuit 3. A capacitor C ₁ is connected to the connection points A ₀ and B _0.
The input of a full-bridge type switching circuit 31 composed of switching elements Q _{1 to} Q ₄ is connected via an input filter 30 composed of The output of the switching circuit 31 is input to a high frequency isolation transformer T _1. The output of the high frequency isolation transformer T ₁ is rectifiers D _{1 to} D ₄
Is input to the full-bridge type rectifier circuit 32, and the output of the full-bridge type rectifier circuit 32 is passed through an output smoothing circuit 33 including a smoothing coil L ₁ and a smoothing capacitor C ₂ to a connection point A. Given to ₁ and B ₁ .

FIG. 3 is a circuit diagram showing the configuration of the DC / AC conversion circuit 4. The inputs of a full-bridge type switching circuit 34 composed of switching elements Q _{11 to} Q ₁₄ are connected to the connection points A ₁ and B ₁ , and the output of the full-bridge type switching circuit 34 is the coils L ₁₁ , L ₁₂ and It is applied to the connection points A ₂ and B ₂ via an output filter 35 composed of a capacitor C ₁₁ .

The switching elements Q _{1 to} Q ₄ and Q ₁₁
Each of Q ₁₄ to Q ₁₄ is configured by using an element such as a bipolar transistor, a field effect transistor, or a power transistor.

The operation of the interconnection type power conversion device 1 thus configured will be described below. First, solar cell 1
00 is excited by sunlight and outputs DC power to its electrodes (+ and −) P and N. Then, this output power is input to the interconnection type power converter 1 via the input terminals A _IN and B _IN . The input relay 2 uses the control power supply 7 to control the circuit 6
After the power supply output to be supplied to the control circuit 6 is established and the control circuit 6 is activated, the control circuit 6 is controlled by the signal SR ₁ output from the control circuit 6 (first function of the control circuit 6). When the input relay 2 is turned on, the output of the solar cell 100 is input to the DC-DC conversion circuit 3 via the relay 2.

The output of the solar cell 100 input to the DC-DC conversion circuit 3 is input to the full bridge type switching circuit 31 via the input filter 30. Switching element Q forming the full-bridge type switching circuit 31
The two switching element pairs of ₁ , Q ₄ and Q ₂ , Q ₃ are alternately subjected to switching control of conduction by signals S ₁₄ and S ₂₃ described later to generate high frequency power. This high frequency power is input to the high frequency isolation transformer T ₁ to excite it. Then, the transformed high-frequency power is output from the high-frequency insulation transformer T ₁ , the output is subjected to full-wave rectification by the rectifier circuit 32, and further converted into DC power through the output smoothing circuit 33.

Here, the switching frequency of the full-bridge type switching circuit 31 is set at 20 or higher than the audible frequency band.
The amount of current flowing through the switching circuit 31 can be changed by changing the ratio (= duty ratio) of the conduction time of the switching elements Q _{1 to} Q ₄ in one cycle with a frequency of around kilohertz. That is, the solar cell 10
When viewed from the 0 side, the input impedance of the DC-DC conversion circuit 3 changes.

Based on this, the operation in which the DC-DC conversion circuit 3 tracks and inputs the maximum output power of the solar cell will be described. FIG. 4 shows the output voltage-current characteristic curve (I) of the solar cell and the input voltage of the DC-DC conversion circuit 3.
It is the diagram which superimposed and represented the electric current characteristic (II). Since the slope of the straight line representing the input voltage-current characteristic (II) of the DC-DC conversion circuit 3 represents the input impedance of the DC-DC conversion circuit 3, the input voltage of the DC-DC conversion circuit 3 will be described below. -The current characteristic (II) is called the input impedance characteristic.

The output of the solar cell 100 having the output voltage-current characteristic (I) represented by the curve in FIG. 4 has the input impedance characteristic (II) represented by the straight line in FIG.
When the input of the DC conversion circuit 3 is connected, the output power of the solar cell 100 (that is, the input power of the DC-DC conversion circuit 3)
Is the electric power obtained from the product of the voltage and the current determined at the intersection P of these two characteristic lines. In other words, by changing the input impedance of the DC-DC conversion circuit 3, the power input from the solar cell 100 to the interconnection power conversion circuit 1 can be controlled.

The solar cell maximum output power tracking function of the DC-DC conversion circuit 3 focuses on this point, and the output voltage and current of the solar cell 100 (that is, the input voltage V _{in of the} DC-DC conversion circuit 3 and The current I _in ) is monitored at any time, and the control circuit 6 controls the input impedance of the DC-DC conversion circuit 3 so that the product of the output voltage and the output current of the solar cell 100 becomes maximum (the first of the control circuits 6). 2 functions).

Here, the input impedance control of the DC-DC conversion circuit 3, which is the second control function of the control circuit 6, will be described. FIG. 5 is a circuit block diagram of an input impedance control unit incorporated in the control circuit 6, and
FIG. 6 shows the MP which constitutes this input impedance control unit.
It is a flowchart showing the operation of U21.

The output of the solar cell 100, that is, the input voltage V _in and the current I _in of the DC-DC conversion circuit 3 are converted into digital quantities by the A / D converter 20 and input to the MPU 21. The input voltage V _in and the current I _in input to the MPU 21 are stored in variables V and I, respectively (steps S12a and S12b). The MPU 21 calculates the product of these variables V and I to obtain the electric power P ₂ (step S
13), the magnitude of the previous power calculation result P ₁ is compared (step S14). In the initial state, zero is stored in the variable P ₁ that stores the previous power calculation result (step S11), and the control voltage signal S to be described later is also stored.
Zero is also stored in _t so that the initial input impedance of the DC-DC conversion circuit 3 becomes infinite (step S11).

[0040] of the comparison result, when the direction of power P ₂ which is calculated this time greater (step S14, Yes), causing the control voltage signal S _t is increased minute (step S15a).
Conversely, in the case towards the power P ₂ computed current is small (Step S14, No), reduces fine control voltage signal S _t (step S15b).

Then, the content of the variable P ₁ which stores the previous power calculation result is updated to the content of the power P ₂ calculated this time (step S16), and the next monitored input voltage V _in and current I _in Wait for input.

The D / A converter 22 converts the control voltage signal S _t , which is updated based on the magnitude comparison result of the electric powers P ₂ and P ₁ , into an analog amount and outputs it to one input of the comparator 24. The triangular wave signal is supplied from the triangular wave signal generating circuit 23 to the other input of the comparator 24 as a reference signal. Then, the comparator 24 compares the reference signal with the control voltage signal S _t converted into the analog amount to generate a clock signal which is a PWM (Pulse Width Modulation) wave. The pulse distributor 25 inputs this clock signal and generates clock signals S ₁₄ and S ₂₃ . These clock signals S ₁₄ and S ₂₃ have a duty ratio according to the magnitude of the control voltage signal S _t . And
The clock signal S ₁₄ controls the conduction of the switching elements Q ₁ and Q ₄ , and the clock signal S ₂₃ controls the conduction of the switching elements Q ₂ and Q ₃ .

When the pulse distributor 25 generates the clock signals S ₁₄ and S ₂₃ , the duty ratios of the respective signals are the same, but the switching elements Q ₁ , Q ₄ and Q are the same.
_A constant phase difference is provided between the clock signals S ₁₄ and S ₂₃ so that the two switching element pairs of ₂ and Q ₃ do not conduct at the same time.

In the case of this embodiment, the clock signals S ₁₄ ,
When S ₂₃ is at a high level (H), the switching elements Q _{1 to} Q ₄ are turned on under the control of the respective clock signals, so that the duty ratio expresses the ratio of the high level period of the signal. The clock signals S ₁₄ and S
The increase of the duty ratio of ₂₃ brings about the decrease of the input impedance of the DC-DC conversion circuit 3.

As described above, in the initial state, the input impedance of the DC-DC conversion circuit 3 is set to be infinite. Further, as understood from FIG. 4, in this initial state, the current flowing into the DC-DC conversion circuit 3 is zero, and the electric power input from the solar cell 100 to the DC-DC conversion circuit 3 is also zero. Therefore, immediately after the control circuit 6 operates, the input impedance of the DC-DC conversion circuit 3 is controlled so as to gradually decrease from infinity. As the input impedance decreases, the output power of the solar cell 100, that is, the power input to the DC-DC conversion circuit 3 increases, and reaches the solar cell maximum output power point P _max .

Further, the input impedance of the DC-DC conversion circuit 3 is controlled so as to decrease, but when the solar cell maximum output power point P _max is exceeded, the output of the solar cell 100 begins to decrease, so the control circuit 6 Controls the control voltage signal S _t slightly and controls the input impedance of the DC-DC conversion circuit 3 so that the power input to the DC-DC conversion circuit 3 remains at the solar cell maximum output power point P _max .

The solar cell maximum output power tracking function is realized by the input impedance control operation of the DC-DC conversion circuit 3 by the control circuit 6 as described above. In addition,
The DC conversion circuit 3 has not only a solar cell maximum output power point tracking function but also a function of insulating the solar cell 100 side from the system distribution line 11 side.

Here, the operation when the electric power input from the solar cell 100 exceeds the allowable input of the interconnection type power converter 1 will be described. FIG. 9 shows an interconnected power converter 1
FIG. 3 is a diagram for explaining a solar cell maximum output power point tracking function in a case where a power range that can be input to a power source and a power input to the interconnected power conversion device 1 exceeds the power range that can be input.

Solar cell 100 to interconnection type power converter 1
The power that is input to the circuit is the rated input power (IV) of the circuit because of the performance restrictions of the circuit elements that make up the interconnected power converter 1.
It is prohibited to exceed. Further, due to the restrictions on the circuit operation of the interconnected power converter 1, the interconnected power converter 1 has a constant input voltage range. Further, as understood from FIG. 4, since the output current of the solar cell 100 does not exceed the rated solar cell short-circuit current I _S , the output power of the solar cell 100 is the power determined by the rated short-circuit current I _S ( It does not exceed III). The input power range (hatched area in FIG. 9) of the interconnected power converter 1 is determined from the above three restrictions. Therefore, when the output power-voltage characteristic (V) of the solar cell 100 is within this range, it is possible to track the maximum output point of the solar cell. Also,
Even if the element temperature of the solar cell rises and the voltage at the maximum output point of the solar cell decreases, if the characteristic curve (VI) is within this range, the maximum solar cell The output point can be tracked.

However, as shown in the characteristic curve (VII) of FIG. 9, when the power input to the interconnection type power converter 1 exceeds the allowable input range, the control circuit 6
Increases the input impedance of the DC-DC conversion circuit 3 to stop tracking the maximum output power point P _max of the solar cell, and moves the input power point from A _a to A _b . As a result, the electric power input from the solar cell 100 to the DC-DC conversion circuit 3 is limited, and the interconnection type power conversion device 1 is protected from damage due to excessive input power.

Next, the operation of the DC-AC conversion circuit 4 for inputting the DC output voltage V _C of the DC-DC conversion circuit 3 will be described. DC output voltage V of DC-DC converter circuit 3
_C is a DC-AC conversion circuit 4 via connection points A ₁ and B _1.
Is input to the full bridge type switching circuit 34 and is converted into AC power. The AC power is further filtered by the output filter 35 to remove unnecessary frequency components, and is output via the connection points A ₂ and B ₂ .

Here, the output voltage V _C of the DC-DC conversion circuit 3 is obtained by the following equation (1), and in the output characteristics of the solar cell 100, in the region from the output open voltage side to around the maximum output point, It shows almost constant voltage characteristics.

V _C = V _IN × D × N2 / N1 (1) However, D: Duty ratio N1; Number of windings on the primary side of the high frequency insulation transformer T ₁ N2; High frequency insulation transformer T Number of secondary windings of ₁

Therefore, in this region, the amount of decrease of the input voltage V _in with respect to the amount of increase of the duty ratio D of the signals S ₁₄ and S ₂₃ for controlling the conduction of the switching circuit 31 is small. Therefore, when the output of the DC-DC converter circuit 3 is unloaded (that is, the output is open), the output voltage V _C rises according to the transformation ratio of the high frequency insulation transformer T ₁ .

However, the input impedance of the DC / AC conversion circuit 4 functions as an output load of the DC / DC conversion circuit 3, and the output voltage V _{C of the} DC / DC conversion circuit 3 does not exceed the preset voltage V _CONST. First, the control circuit 6 controls the output current I _out of the DC-AC conversion circuit 4. That is, the DC-AC conversion circuit 4 operates to maintain the voltage V _C at a constant voltage by controlling the amount of discharging the input current as the output current I _out by the control circuit 6. The current I _out control function of the control circuit 6 is a third control function of the control circuit 6 described later.

Here, the voltage V _CONST is a value designed and determined so that the output voltage of the DC-AC conversion circuit 4 cooperates with the voltage on the interconnection line side. Thus, the voltage V _C
As a result, the output voltage of the interconnection type power conversion circuit 1 can be kept constant, and cooperation with the voltage on the system distribution line side becomes possible.

Here, the current I _out control function, which is the third control function of the control circuit 6, will be described. Adjustment of the amount of current discharged from the DC-AC conversion circuit 4 as the current I _{out is} as follows.
This is realized by controlling the time during which the switching elements Q _{11 to} Q ₁₄ forming the full-bridge type switching circuit 34 are conducted by the control circuit 6.

FIG. 7 shows the current I incorporated in the control circuit 6.
FIG. 8 is a circuit block diagram of the _out control unit, and FIG. 8 is a flowchart showing the operation of the MPU 51 forming the current I _out control unit.

The operation of controlling the output current I _out is also the same as the principle of controlling the input impedance in the DC-DC converting circuit 3. This will be described below. Control circuit 6
The output voltage V _C of the DC-DC conversion circuit 3 input as information to the A / D converter 50 is converted into a digital amount and input to the MPU 51. Information on the voltage V _C input to the MPU 51 is stored in the variable VC ₂ (step S22). The MPU 51 compares the content of the variable VC ₂ with the preset voltage V _min (step S2).
3). This voltage V _min is the minimum voltage that can be taken by the voltage V _C , and is set so that the voltage V _C does not exceed the above-mentioned V _CONST .

As a result of the comparison, if it is determined that the content of the variable VC ₂ does not exceed the preset voltage V _min (step S23, No), the control voltage signal S _a is reset to zero (step S23). S24), waiting for input of the next monitored voltage V _C. If it is determined that the variable VC ₂ is larger than V _min (step S23, Yes),
Further, the variable VC ₂ is compared with the variable VC ₁ in which the previous monitor value of the voltage V _C is stored (step S25).
As a result of the comparison, when it is determined that the variable VC ₂ is larger (step S25, Yes), the control voltage signal S _a is slightly increased (step 26a). Conversely, if it is determined to be small, it is slightly reduced (step S26b).

Then, the content of the variable VC ₁ for storing the previous monitoring result is stored in the variable VC ₂ for storing the result of the current monitoring.
Is updated (step S27), and the input of information on the voltage V _C to be monitored next is awaited.

In the initial state, zero is stored in the variable VC ₁ for storing the information on the previously monitored voltage V _C (step S21), and the control voltage signal S
_a DC - zero as the input impedance of the AC conversion circuit 4 becomes infinite is set (step S2
1).

The D / A converter 52 has the voltages VC ₁ and V
The control voltage signal S _a updated based on the magnitude comparison result of C ₂ is converted into an analog amount and supplied to the mixer 58.

On the other hand, the reference sine wave signal generation circuit 54 inputs the output voltage V _out of the DC-AC conversion circuit 4 as information and generates a reference sine wave signal. The reference sine wave signal and the control voltage signal S _a converted into the analog amount are mixed by the mixer 5
It is mixed by 8 and is supplied to one input of the error amplifier 55 which _receives the information of the output current I _out of the DC-AC conversion circuit 4 as the other input. The output signal obtained from the error amplifier 55 in this manner is generated such that the output current waveform of the interconnected power converter 1 becomes a sine wave.

The comparator 56 is the triangular wave signal generation circuit 5
The triangular wave signal output from 3 is compared with the output signal of the error amplifier 55 to generate a clock signal which is a PMW (Pulse Width Modulation) wave, and the pulse distributor 57 inputs this clock signal and receives the clock signal S _114. And S ₁₂₃ are generated. The signals S ₁₁₄ and S ₁₂₃ generated in this way
Has a duty ratio according to the magnitude of the control voltage signal S _a . Then, the conduction time of the switching circuit 34 is controlled in accordance with the increase or decrease of the control voltage signal S _a, the output current I _out is increased or decreased. These clock signals _S114 and S114
The driving of the switching circuit 34 by ₁₂₃ is the same as that of the switching circuit 31, and the description thereof is omitted.

The frequencies of the clock signals S ₁₁₄ and S ₁₂₃ are determined so that the power output from the interconnection type power converter 1 has a frequency component that cooperates with the grid distribution line 11 side.

In this way, the control circuit 6 monitors the increase / decrease in the voltage V _C and adjusts the current I _out . As a result, DC-
In the AC conversion circuit 4, the voltage V _C is the voltage V _min and the voltage V _CONST.
It operates so as to be held at a substantially constant voltage between and.
Thereby, the DC-AC conversion circuit 4 is connected to the system distribution line 11
The output current I _out is supplied to the system distribution line 11 via the interconnection relay 5 while maintaining the output voltage V _out in cooperation with the side voltage.

Here, the interconnection relay 5 includes the system distribution line 11
The voltage and frequency are normal, and after the output of the DC-AC conversion circuit 4 is established, it is controlled and turned on by the control circuit 6 (fourth control function of the control circuit 6).

As described above, the DC output generated by the solar cell 100 is converted into an AC voltage in which the voltage and frequency are coordinated with the power on the system distribution line side and appears at the output terminals A _OUT and B _OUT .

Next, the operation control (fifth function of the control circuit 6) when the interconnection type power conversion device 1 cannot operate in cooperation with the connected system distribution line will be described. First
The case where the system voltage and the frequency of the system distribution line deviate from their respective set values will be described. In this case, the control circuit 6 releases the interconnection relay 5 and stops the switching operations of the switching circuits 31 and 34 of the DC-DC conversion circuit 3 and the DC-AC conversion circuit 4 to operate the interconnection type power conversion device 1. It is controlled to disconnect from the system distribution line 11 and stop the operation.

Secondly, a case will be described in which, for example, a circuit breaker connected between the power conversion device 1 and the system distribution line 11 is opened. In this case, if the load between the V ₁ and V ₂ 100V lines of the system distribution line 11 is unbalanced, an overvoltage is applied to the load connected to the 100V line. In order to protect the load due to this overvoltage, the control circuit 6 monitors the voltage (V ₁ , V ₂ ) of the distribution line with respect to the neutral line of the system distribution line 11, and when this monitor voltage exceeds a certain value. In addition, the control circuit 6 releases the interconnection relay 5 so that the interconnection type power converter 1 is connected to the system distribution line 1
By disconnecting from 1 and stopping the switching operations of the switching circuits 31 and 34 of the DC-DC conversion circuit 3 and the DC-AC conversion circuit 4, respectively, the operation of the apparatus is controlled to be instantaneously stopped. As described above, the control circuit 6 has, as a fifth control function, a control function of monitoring the voltage and the frequency of the system distribution line and stopping the operation of the interconnection type power conversion device 1.

[0072]

In the interconnected power converter according to the first and second aspects, the output of the solar cell is input to the DC-DC conversion circuit, and the input impedance of this DC-DC conversion circuit is
Since the maximum output power of the solar cell is controlled so as to be input, the DC output of the solar cell can be efficiently converted into AC power, and the output of the solar cell can be effectively used.

Further, in the interconnection type power conversion device of the second aspect, since the high frequency insulation transformer is used instead of the commercial insulation transformer, the size and weight of the device can be greatly reduced.

Furthermore, in the interconnected power converter of claim 3, when the overpower is input from the solar cell, the input impedance of the interconnected power converter is increased. The power input to the device can be limited, and the device can be prevented from being damaged by the input of excessive power.

Furthermore, in the interconnection type power converter of claim 4, when the interconnection operation cannot be maintained in cooperation with the system distribution line or when an overvoltage occurs in the system distribution line,
Since the control circuit controls the operation of the device to stop,
There is no need to install an interconnection protection device or an overvoltage protection relay,
Further size reduction and cost reduction of the device can be achieved.

[Brief description of drawings]

FIG. 1 is a system block diagram showing a configuration of a photovoltaic power generation system to which the present invention is applied.

FIG. 2 is a circuit diagram showing a configuration of a DC-DC conversion circuit.

FIG. 3 is a circuit diagram showing a configuration of a DC-AC conversion circuit.

FIG. 4 is a diagram in which an output voltage-current characteristic curve (I) of a solar cell and an input voltage-current characteristic (II) of a DC-DC conversion circuit are overlaid.

FIG. 5 is a circuit block diagram of an input impedance control unit in the control circuit.

FIG. 6 is a flowchart showing the operation of the MPU 21.

FIG. 7 is a circuit block diagram of a voltage V _C control unit in the control circuit.

FIG. 8 is a flowchart showing the operation of the MPU 51.

FIG. 9 is a diagram for explaining an inputtable power range and a solar cell maximum output power point tracking function of the interconnected power converter.

FIG. 10 is a system block diagram showing a photovoltaic power generation system to which a conventional interconnected power converter is applied.

FIG. 11 is a system block diagram showing a photovoltaic power generation system to which a conventional interconnected power conversion device configured by using a high-frequency insulation transformer is applied.

[Explanation of symbols]

1 Connection type power converter 2 Input relay 3 DC-DC converter 4 DC-AC converter 5 Connection relay 6 Control circuit 7 Control power supply 8,9 Current sensor 10 Pole transformer 11 Single-phase 3-wire system distribution wire 30 input filter 31, 34 a full-bridge type switching circuit 32 full-bridge rectifier 33 output smoothing circuit 35 outputs the filter 103 system power source C ₁ ~C _2, C ₁₁ capacitor D ₁ to D ₄ rectifier L _1, L _11, L ₁₂ coil _{Q 1 ~Q 4, Q 11 ~Q} 14 switching elements T _1, T ₂ RF isolation transformer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication H02M 7/48 9181-5H H02M 7/48 R

Claims (4)

[Claims] 1. A DC-DC conversion circuit for inputting DC output of a solar cell to convert DC-DC, and a DC-AC conversion circuit for inputting output of the DC-DC conversion and DC-AC conversion. And a control circuit, wherein the control circuit calculates the power of the DC output of the solar cell, and controls the input impedance of the DC-DC conversion circuit based on the calculation result. apparatus. 2. A direct current-direct current conversion circuit receives a solar cell output, converts it into high frequency power and outputs it, a high frequency isolation transformer which inputs the output of the switching circuit, and the high frequency isolation transformer. And a rectifying circuit for rectifying the output of the switching circuit, wherein the conduction time of the switching circuit is controlled by the control circuit to control the input impedance of the switching circuit. apparatus. 3. The control circuit, when the output power of the solar cell exceeds the allowable input of the DC-DC conversion circuit, the DC-
The interconnection type according to claim 1, wherein the input impedance of the DC-DC conversion circuit is controlled within a range in which an input of the DC-DC conversion circuit does not exceed an allowable input current and an allowable input power of the DC-DC conversion circuit. Power converter. 4. The control circuit comprises detection means for detecting the voltage of the system distribution line or its frequency, and one or more of which the control circuit controls its operation based on the result detected by the detection means. 2. The interconnection type power conversion device according to claim 1, wherein the operation of the element circuit is temporarily stopped.