JPH10207559A - Link type power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a link type power converter capable of effectively utilizing the output of a solar battery and increasing a device output. SOLUTION: The link type power converter 1 is constituted of a main circuit part provided with an input relay 2, a converter circuit 3 having a switching element, an inverter circuit 4 having a switching element, and a link relay 5, a control circuit 6 for controlling the main circuit part and current sensors 8, 9 for respectively detecting the input current Iin of the circuit 3 and the output current Iout of the circuit 4. The control circuit 6 detects the output voltage and current of the solar battery, changes switching frequency so as to maximize the output power of the solar battery and controls the input impedance of the circuit 3.

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. 9 is a system block diagram showing a photovoltaic power generation system to which the interconnection type power converter disclosed in Japanese Patent Application Laid-Open No. 2-81107 is applied. The interconnection type power converter 111 converts the DC output of the solar cell 100 into a voltage using a DC-DC converter 112, further converts it into an AC power using an AC converter 113, and supplies power to the system power supply 103. The voltage and frequency are converted into coordinated power and output to the distribution line 106.

[0003]

In general, the output of a solar cell fluctuates depending on the solar radiation intensity of the solar cell and the element temperature of the solar cell. The interconnected power converter disclosed in Japanese Patent Application Laid-Open No. 81107/1990 makes the output of the solar cell constant, and therefore cannot extract the maximum output power from the fluctuating output of the solar cell. There is a problem that the power generated by the battery cannot be used effectively. Also,
The DC-DC conversion circuit of this interconnection type power converter is of a forward type, and has a problem that the output capacity cannot be increased.

[0004] The present invention has been made in view of such a problem, and it is possible to effectively use the output of a solar cell and to provide an interconnected type capable of outputting twice the output of the interconnected power converter. An object is to provide a power converter.

[0005]

According to a first aspect of the present invention, the output of a solar cell is stabilized by a switching operation of a switching element into a DC power of a DC voltage in a fixed range.
A converter circuit for performing DC conversion, an inverter circuit for receiving an output of the converter circuit and performing DC-AC conversion to the same AC power as that of a system distribution line, and detecting an output voltage and an output current of the solar cell; A control circuit that calculates a solar cell output power, which is an input power of the converter circuit, and controls an input impedance by varying a switching frequency with respect to the converter circuit so that the solar cell output power is maximized. It is an interconnection type power converter characterized by the following.

According to a second aspect of the present invention, there is provided the interconnection type power converter according to the first aspect, wherein the converter circuit includes four switching elements for converting the output of the solar cell into high-frequency power. -Type switching circuit, a high-frequency insulating transformer that insulates an input side and an output side for inputting an output of the switching circuit and converts an output voltage to a constant voltage, and rectifies a high-frequency output of the high-frequency insulating transformer to DC. And a rectifier circuit. The control circuit controls the input impedance of the converter circuit by alternately switching two pairs of switching elements at each diagonal of the bridge in the switching circuit.

According to a third aspect of the present invention, there is provided the interconnection type power converter according to the second aspect, wherein the control circuit is configured to switch the pair of switching devices when the output power of the solar cell is smaller than the rated input of the converter circuit. Only one of the elements is operated for high-frequency switching.

According to a fourth aspect of the present invention, there is provided the interconnection type power converter according to the first aspect, wherein the control circuit detects a switching frequency of the converter circuit, and the switching frequency of the converter circuit is set in advance. When the frequency is exceeded, the control circuit temporarily stops the operation of the converter circuit.

According to the first aspect of the present invention, if the input impedance of the converter circuit, which is an output load as viewed from the solar cell side, changes, the operating point of the solar cell changes, and the output power of the solar cell changes in its output characteristic curve. Change along. The control circuit calculates the output power of the solar cell, varies the switching frequency of the converter circuit so as to maximize the output of the solar cell, controls the input impedance, and effectively uses the output of the solar cell.

According to the second aspect of the present invention, since the switching circuit of the converter circuit is a bridge type of four switching elements, like the interconnection type power converter disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2-81107, The output can be double that of the forward mode of the converter circuit using one switching element.

According to the third aspect of the present invention, the control circuit is configured to reduce loss at a low output to a middle output of the converter.
When the output power of the solar cell is lower than the rated input of the converter circuit, only a part of the switching elements of the converter circuit is operated to perform a switching operation to reduce the loss due to the switching elements.

According to a fourth aspect of the present invention, when the switching frequency exceeds a preset maximum switching frequency of the converter circuit, the control circuit temporarily stops operation of the converter circuit. To protect the power converter.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system block diagram illustrating a configuration of a photovoltaic power generation system including an interconnected power conversion device according to the present invention as a component device. The interconnection type power converter 1 converts the DC output generated by the solar cell 100 into a single-phase two-wire 200 V (V _ug ) AC power, and converts the output to a single-phase three-wire 200/100 V system distribution line 11. And 200 V for connection operation. The single-phase three-wire system distribution line 11 is provided with a system power
And the power is transformed to 100V and 200V. That is, the neutral terminal N of the pole transformer 10 is grounded, and a voltage of 100 V (V) is applied between the neutral terminal N and the terminal H.
₁ ) is applied, and 10 is also applied between the neutral terminal N and the terminal L.
0 V (V ₂ ) is applied, and 20
0 V (V _ug ) is applied.

Between the output terminals A _out and B _out of the interconnection type power converter 1, a 200 V
(V _ug ) is output, and the output terminals A _out and B _out are connected to the terminals H and L on the system distribution line side. The interconnection type power conversion device 1 includes a main circuit unit including each element of an input relay 2, a converter circuit 3, an inverter circuit 4, and an interconnection relay 5, a control circuit 6 for controlling the main circuit unit,
Input current I _in of converter circuit 3 and inverter circuit 4
The current sensor 8 and 9 for the output current I _out is detected respectively, and a control power source 7 for supplying a control power to the control circuit 6 by entering part of the power outputted from the solar cell. The input terminals A _in and B _in to which the output of the solar cell 100 is connected are connected to the input terminals 2 a and 2 b of the input relay 2.
Are connected, and the output terminals 2c and 2d of the relay 2 are connected to the input of the converter circuit 3 via the connection points A ₀ and B ₀ .

[0015] In addition, the control to the input terminal A _in and B _in the power supply 7
The output of the control power supply 7 is supplied to the control circuit 6 and used as the operation power supply. On the other hand, the output of the converter circuit 3 is input to the inverter circuit 4 through the connection points A ₁ and B ₁ , and the output of the inverter circuit 4 is input to the input terminal 5 a of the interconnection relay 5 through the connection points A ₂ and B _2. , 5
b. Further, output terminals 5c and 5d of the interconnection relay 5 are connected to terminals A _out and B _out which are output terminals of the interconnection type power converter 1, respectively.

The input terminal A _in and the terminal 2 of the input relay 2
a, the current I _in inputted to the converter circuit 3
Current sensor 8 for detecting provided. In addition, connector relay 5 and the output of the inverter circuit 4 (the connection point A ₂ side)
A current sensor 9 for detecting a current _Iout output from the inverter circuit 4 is provided between the input terminal 5a and the input terminal 5a. The currents I _in and I _out detected by the current sensors 8 and 9 are provided to the control circuit 6 as information.

[0017] The control circuit, the voltage V _in input to the converter circuit 3 from the solar cell 100, the output voltage V _C of the converter circuit 3, the output voltage V of the inverter circuit 4
_out and the output terminals A _out , B of the interconnected power converter 1
_out is connected to the voltage V _{1 of} the single-phase three-wire system distribution line 11,
V ₂ and V _ug are given as information.

Based on these information, the control circuit 6
Relay control signals SR ₁ and SR ₂ are applied to input relay 2 and interconnection relay 5, respectively, and drive signals SC ₁ and SC ₂ are applied to switching elements of converter circuit 3 and inverter circuit 4, respectively. Here, the control circuit 6 has a function of controlling the input / disconnection of the input relay 2, the function of controlling the input impedance of the converter circuit 3, the control of the output current I _out of the inverter circuit 4, and the fourth. Fifth, it has a function of detecting the abnormality of the voltage and frequency of the system distribution line and stopping the power conversion operation of the interconnection type power conversion circuit 1.

FIG. 2 is a circuit diagram showing a configuration of the converter circuit 3. The inputs of a full-bridge switching circuit 31 composed of switching elements Q _{1 to} Q ₄ are connected to the connection points A ₀ and B ₀ via an input filter 30 composed of a capacitor C ₁ . The output of the switching circuit 31 is input to a high frequency isolation transformer T _1. The output of the high-frequency insulating transformer T ₁ is input to the rectifier D ₁ consists to D ₄ full bridge rectifier 32, the output of the full-bridge rectifier 32, a smoothing coil L
_The signal is supplied to connection points A ₁ and B ₁ through an output smoothing circuit 33 composed of ₁ and a smoothing capacitor C ₂ .

FIG. 3 is a circuit diagram showing a configuration of the inverter circuit 4. Switching elements Q are connected to connection points A ₁ and B _1.
11 to Q ₁₄ input of the full bridge type switching circuit 34 is connected composed of, the output of the full-bridge type switching circuit 34 via an output filter 35 comprised of the coil L _11, L ₁₂ and capacitor C ₁₁ Connection point A
₂ , B ₂ . The switching elements Q _{1 to} Q ₄ and the switching elements Q _{11 to} Q ₁₄ are, for example, IGBTs, F
It is configured using elements such as an ET and a power transistor.

The operation of the thus-configured interconnected power converter 1 will be described below. The solar cell 100 outputs DC power excited by sunlight, and the input terminals A _in ,
Is input to the interconnection power converting apparatus 1 via the B _in. After the power supply output supplied to the control circuit 6 by the control power supply 7 is established and the control circuit 6 is activated, the input relay 2
It is introduced under the control of the signal SR ₁ output from. When the input relay 2 is turned on, the output of the solar cell 100 is input to the converter circuit 3 via the relay 2. The output of the solar cell 100 input to the converter circuit 3 passes through the input filter 30 and is supplied to the full-bridge switching circuit 3.
1 is input.

The switching elements Q _{1 to} Q ₄ constituting the full-bridge type switching circuit 31 include signals S ₁ to S ₁ to be described later.
Generating high frequency power is ON / OFF controlled by S _4. The high-frequency power is input to high-frequency insulating transformer T _1, excites them. From the high-frequency insulating transformer T ₁ is output RF power is transformed, full-wave rectifying the output by the rectifier circuit 32, and further converted into DC power via the smoothing circuit 33. The resonance occurs determined by the leakage inductance L _lk capacitor capacitance C _qr and the high-frequency insulating transformer T ₁ of the capacitor C _r. Resonance frequency at this time is a _{f r = 1 / (L lk} · C qr) 1/2.

Here, for example, two of Q ₁ , Q ₄ and Q ₂ , Q ₃
The switching frequency f
_sw (However, f _sw <and f _r) When switching, the resonance current of the resonance frequency f _r is generated, transmitting the power. The magnitude of this power is determined by the magnitude of the switching frequency, and the greater the power, the greater the transmitted power. This means that, when viewed from the solar cell 100 side, the change in the switching frequency changes the ON time of the switching element, resulting in a change in the input impedance of the converter circuit 3.

Based on this, the operation of the converter circuit 3 for tracking and inputting the maximum output power of the solar cell will be described. FIG. 4 is a diagram in which the output voltage-current characteristic curve (I) of the solar cell and the input voltage-current characteristic (II) of the converter circuit 3 are superimposed. Since the slope of the straight line representing the input voltage-current characteristic (II) of the converter circuit 3 represents the input impedance of the converter circuit 3, in the following description, the input voltage-current characteristic (I
I) is called input impedance characteristic.

When the converter circuit 3 having the input impedance characteristic (II) represented by the straight line in FIG. 4 is connected to the output of the solar cell 100 having the output power-current characteristic (I) shown by the curve in FIG. The output power of 100 (that is, the input power of the converter circuit 3) is the 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 converter circuit 3, the solar cell 100
Can control the power input to the interconnection type power conversion circuit 1 from the power supply.

The solar cell maximum output power tracking function of the converter circuit 3 focuses on this point.
0 of the output voltage and current (i.e., the input voltage V _in and the current I _in the converter circuit 3) from time to time monitors, solar cell 1
The control circuit 6 controls the input impedance of the converter circuit 3 so that the product of the output voltage and the output current of 00 becomes maximum.

Here, the input impedance control of the converter circuit 3 will be described. FIG. 5 is a circuit block diagram of an input impedance control unit incorporated in the control circuit 6. The input impedance control unit includes an A / D converter 20, an MPU 21, a logic circuit 22, and drive circuits 23 to 26. FIG. 6 is a flowchart showing the operation of the MPU 21 constituting the input impedance control unit. The input impedance control operation will be described below.

[0028] In the initial state, the memory of the MPU 21, is stored zero as the variable P ₁ storing the previous power calculation result (step S11), and also later-described switching frequency setting signal S _f as well converter circuit 3
Is stored so that the initial input impedance of the data becomes infinite (step S11). Now, the input voltage V _in and the current I _in the output of the solar cell 100, i.e. the converter circuit 3, by the A / D converter 20 is converted into a digital quantity is input to the MPU 21. Voltage V _in and the current I _in input to the MPU 21 is stored as the value of the variables V and I in the memory in the MPU 21. (Steps S12a and S12b). MPU21 obtains power P ₂ calculates the product of the variables V and I (step S1
3), the previous power calculation result P ₁ and to magnitude comparison (step 14). The comparison result, when the direction of power P ₂ which is calculated this time large increases the switching frequency setting signal S _f (step S15a).

Further, conversely, in the case towards the power P ₂ computed this time is small (step S14), and reduces the switching frequency setting signal S _f (step S15b). Last, to update the contents of the power P ₂ obtained by calculating this time the contents of the variable P ₁ storing the power calculation result (step S16), and
Input voltage V _in to then be monitored, waiting for the input of the input current I _in. And switching frequency setting signal S _f obtained by MPU 21, in accordance with the input power value, the ON / OFF signals respectively to the switching element generated by the logic circuit 22, each of the switching elements Q ₁ through the drive circuit 23 to 26 to Q Turn ₄ ON / OFF.

Hereinafter, a method of generating an ON / OFF signal of the switching element in the logic circuit 22 will be described. The input power is 1/1 / the rated input power of the converter circuit 3.
The switching pattern is changed between less than 2 and 1/2 or more. Here, the switching pattern is divided by の of the rated input power of the converter circuit 3, but this is an example, and there is no problem if the switching pattern is divided by other values.

When the input power of converter circuit 3 is less than 1/2 of the rated input, switching elements Q ₁ and Q ₄ are turned off.
F, Q ₂ ON, Q ₃ switching frequency setting signal f _sw
Operation for a certain period according to the switching frequency set in
After that, the switching elements Q ₂ and Q ₃ are turned off and Q ₁ is turned off.
N, driving a certain period by switching frequency set to Q ₄ at the switching frequency setting signal f _sw. The operation is performed by repeating this alternately. The switching elements Q ₁ and Q ₄ are OFF, Q ₂ is in switching operation, and Q ₃ is ON.
It may be. Further, the switching elements Q ₂ and Q ₃ are O
In the case of FF, even if Q ₁ is ON and Q ₄ is switching, Q ₁
There may be a switching, Q ₄ is ON.

When the input power of converter circuit 3 is equal to or more than の of the rated input, switching elements Q ₁ and Q ₄ and Q ₂
And by Q ₃ the pairs respectively, alternately operated by the switching frequency set by the switching frequency setting signal f _sw. In the case of the present embodiment, an increase in the switching frequency setting signal is an increase in the switching frequency of the switching element of the converter circuit 3, and the ON state of the switching element is also increased.
Input impedance becomes small.

As described above, in the initial state, the input impedance of the converter circuit 3 is set to infinity. Further, as can be seen from FIG. 4, in this initial state, the power flowing into the converter circuit 3 is zero,
Immediately after the operation of the control circuit 6, the input impedance of the converter 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 converter circuit 3, increases, and the solar cell maximum output power point P _max
To reach.

Further, the input impedance of the converter circuit 3 is controlled to decrease. However, after the maximum output power point _Pmax of the solar cell, the output power of the solar cell 100 starts to decrease. is slightly decreased the frequency setting signal S _f, power input to the converter circuit 3 is to remain in the solar cell maximum output power point P _max, to control the input impedance of the converter circuit 3. Converter circuit 3 by control circuit 6 as described above
, A solar cell maximum output power point tracking function is realized.

The converter circuit 3 has a function of insulating the solar cell 100 and the system power distribution line 11 in addition to the function of tracking the maximum output power point of the solar cell. Further, the control circuit 6 detects the switching frequency as needed,
Control is performed so that the switching frequency does not exceed the preset maximum frequency. If the switching frequency exceeds the maximum frequency, the switching of the converter circuit 3 is stopped, and the input power of the converter becomes equal to or higher than the rated input. To protect the

Next, the DC output voltage V _C of the converter circuit 3
The operation of the inverter circuit 4 for inputting the following will be described.
The DC output voltage V _C of the converter circuit 3 is input to the full-bridge switching circuit 34 of the inverter circuit 4 via the connection points A ₁ and B ₁ and is converted into AC power. The AC power is further remove unwanted frequency components in the output filter 35, it is outputted via the node A ₂ and B _2.
The voltage V _CONST is a value designed and determined so that the output voltage of the inverter circuit 4 cooperates with the voltage on the interconnecting distribution line side, and the control circuit 6 controls the output voltage so as to be the voltage V _CONST . As a result of controlling the voltage V _CONST to be constant, the output voltage of the interconnected power conversion circuit 1 can be kept constant, and coordination with the voltage on the system distribution line side is possible.

Here, the current I _out control function as the third control function of the control circuit 6 will be described. Adjustment of the amount of current discharged from the inverter circuit 4 as the current I _out is implemented is controlled by the control circuit 6 the time when the switching element Q ₁₁ to Q ₁₄ constituting the full-bridge type switching circuit 34 becomes conductive.

FIG. 7 shows the current I incorporated in the control circuit 6.
It is a circuit block diagram of an _out control part. The current I _out control unit includes an A / D converter 50, an MPU 51, a D / A
The configuration includes a converter 52, a triangular wave signal generation circuit 53, a reference sine wave signal generation circuit 54, an error amplifier 55, a comparator 56, a pulse distributor 57, and a mixer 58. FIG. 8 is a flowchart showing the operation of the MPU 51 constituting the current I _out control unit. The current I _out control operation will be described below.

The operation of controlling the output current _Iout is also the same as the principle of input impedance control in converter circuit 3. In the initial state, the memory in the MPU 51, zero is stored as a variable VC ₁ is information of the voltage V _C of the previously monitored (step S2
1). Further, the control voltage signal S _a is zero so that the input impedance of the inverter circuit 4 becomes infinite is set (step S21). The output voltage V _C of the converter circuit 3 input as information to the control circuit 6 is A / D
Converted to a digital quantity by the converter 50 and
1 is input. Information of the voltage V _C which is input to the MPU51 is stored as the value of a variable VC ₂ in the memory (step S22). MPU51 compares the magnitude of the preset voltage V _min with the contents of the variable VC ₂ (step S23). This voltage V _min is the minimum voltage that the voltage V _C can take, and the maximum voltage of the voltage V _C is the voltage V _C described above.
_It is determined not to exceed _CONST .

[0040] The result of the comparison, when the contents of the variable VC ₂ is determined not to exceed the voltage V _min, which is set in advance (step S23), zero control voltage signal S _a is reset (Step S24) , The next monitored voltage V
Wait for _C input. Further, when the direction of the variable VC ₂ is determined to be greater than V _min (step S23), further variables VC
₂ monitor value of the previous voltage V _C is the stored variables VC ₁ and magnitude are compared (step S25). Result of the comparison, when the direction of the variable VC ₂ is determined to be larger (step S25), and the control voltage signal S _a is increased minute (step 26a). Conversely, if it is determined to be small, it is slightly reduced (step S26b). Then, update the contents of the variable VC ₂ to store the results of monitoring the current contents of variables VC ₁ for storing a previous monitor result (step S2
7) waits for input of information of the voltage V _C which is then monitored.
Incidentally, D / A converter 52 converts the control voltage signal S _a which is updated based on the magnitude comparison result of the voltage VC ₁ and VC ₂ in analog quantity, it gives the mixer 58.

On the other hand, the reference sine wave signal generation circuit 54 inputs the output voltage V _out of the inverter circuit 4 as information,
Generate a reference sine wave signal. From this reference sine wave signal and the control voltage signal S _a which is converted into an analog quantity are mixed by the mixer 58, one input of the error amplifier 55 to the information of the output current I _out of the inverter circuit 4 and the other input Given to. 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 a triangular wave signal generating circuit 5
3 is compared with the output signal of the error amplifier 55 to generate a clock signal of PWM (Pulse Width Modulation), and the pulse distributor 57 receives the clock signal and inputs the clock signal _S114 and the clock signal _S114. Generate _S123 . Such signal S ₁₁₄ and S ₁₂₃ produced by the will to have a duty ratio corresponding 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 _S114 and _S123 are determined so that the power output from the interconnected power converter 1 has a frequency component that cooperates with the system distribution line 11. Thus, the control circuit 6 adjusts the current I _out by monitoring the increase or decrease of the voltage V _C. As a result, the inverter circuit 4 operates so that the voltage V _C is maintained at a substantially constant voltage between the voltage V _min and the voltage V _CONST . As a result, the inverter circuit 4 holds the output voltage V _out coordinated with the voltage on the system distribution line 11 side, and
The output current I _out is supplied to the system distribution line 11 through

Here, the interconnection relay 5 is connected to the system distribution line 11.
After the voltage and frequency of the inverter circuit 4 are normal and the output of the inverter circuit 4 is established, the circuit 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 power, voltage, and frequency of the system distribution line are coordinated, and appears at the output terminals A _OUT and B _OUT .

[0045]

According to the first aspect of the present invention, the control circuit comprises:
Since the output power of the solar cell is calculated and the input impedance of the converter circuit is controlled so that the output of the solar cell is maximized, the output of the solar cell can be used effectively.

According to the second aspect of the present invention, the switching circuit is a bridge type of four switching elements, and the power flowing through the converter circuit is controlled by the switching frequency of the switching elements. The output can be twice as large as the forward method of the circuit, and the output of the solar cell can be used effectively.

According to the third aspect of the present invention, when the output power of the solar cell is low, the control circuit causes only one of the pair of switching elements of the converter circuit to perform the high-frequency switching operation. At the time of medium output, the loss due to the operation of the switching element can be reduced, and the output of the solar cell can be used effectively.

According to the fourth aspect of the present invention, when the switching frequency exceeds a preset maximum switching frequency of the converter circuit, the control circuit temporarily stops operation of an element circuit that controls the operation of the converter circuit. , It is possible to protect the interconnected power converter.

[Brief description of the drawings]

FIG. 1 is a system block diagram illustrating a configuration of a photovoltaic power generation system including an interconnected power conversion device according to the present invention as a component device.

FIG. 2 is a circuit diagram showing a configuration of a converter circuit.

FIG. 3 is a circuit diagram showing a configuration of an inverter circuit.

FIG. 4 is a diagram in which an output voltage-current characteristic curve of a solar cell and an input voltage-current characteristic of a converter circuit are superimposed.

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

FIG. 6 is a flowchart illustrating an operation of an MPU configuring the input impedance control unit.

FIG. 7 is a circuit block diagram of a current I _out control unit incorporated in the control circuit 6.

FIG. 8 is a flowchart showing the operation of the MPU 51 constituting the current I _out control unit.

FIG. 9 is a system block diagram illustrating a photovoltaic power generation system to which a conventional power converter is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Interconnection type power converter 2 Input relay 3 Converter circuit 4 Inverter circuit 5 Interconnection relay 6 Control circuit 7 Control power supply 8, 9 Current sensor 10 Pole transformer 100 Solar cell 103 System power supply

Claims (4)

[Claims] 1. A converter circuit for converting the output of a solar cell to DC power of a stable DC voltage in a certain range by a switching operation of a switching element, and a system distribution line by receiving an output of the converter circuit. An inverter circuit that performs DC-AC conversion to the same AC power; and detects an output voltage and an output current of the solar cell to calculate a solar cell output power that is an input power of the converter circuit, and the solar cell output power is maximum. And a control circuit for varying the switching frequency to control the input impedance of the converter circuit. 2. The converter circuit includes: a bridge-type switching circuit including four switching elements for converting an output of the solar cell into high-frequency power; and an input side and an output side for inputting an output of the switching circuit. A high-frequency insulating transformer that insulates and converts an output voltage to a constant voltage, and a rectifier circuit that rectifies a high-frequency output of the high-frequency insulating transformer into a direct current, wherein the control circuit includes a bridge in the switching circuit. 2. The interconnected power converter according to claim 1, wherein the input impedance of the converter circuit is controlled by alternately switching two pairs of diagonal switching elements one by one. 3. The control circuit according to claim 2, wherein when the output power of the solar cell is smaller than the rated input of the converter circuit, only one of the pair of switching elements performs a high-frequency switching operation. Interconnected power converter. 4. The control circuit detects a switching frequency of the converter circuit, and when the switching frequency exceeds a preset maximum switching frequency of the converter circuit, the control circuit temporarily stops the operation of the converter circuit. The interconnected power converter according to claim 1, wherein: