JP2002112461A - Power converter and power generator - Google Patents

Abstract

(57) [Summary] [Problem] When supplying AC modules to Japan, it is necessary to prepare two types of output, 100V and 200V, and if it includes foreign countries, it will correspond to more various types of system voltage A possible AC module must be manufactured. SOLUTION: A control circuit 104 operates an inverter circuit 103 and / or a transformation ratio of a transformation circuit 105 and a switch 108 based on a system voltage and a connection state of a power system 110.
Control the opening and closing of

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter and a power generator, for example, a power converter such as an inverter which can be connected to a power system, and a power output from a DC power supply such as a solar cell or a storage battery. To a power generator which converts AC power into AC power by a power converter and supplies the AC power to a load or a power system.

[0002]

2. Description of the Related Art In recent years, due to efforts to address environmental issues,
The DC power generated by the solar cells is converted into AC power by an inverter, and the AC power is converted into a house load (hereinafter simply referred to as “load”) and / or a commercial power system (hereinafter, referred to as “load”).
A large number of photovoltaic power generators for supplying power to the "system" are installed.

[0003] These photovoltaic power generation devices have also attracted attention as emergency power supplies in the event of a disaster such as an earthquake. In recent years, there are many photovoltaic power generators that can be disconnected from the grid and operated independently to supply power to a load in the event of a power failure due to an earthquake, system failure or maintenance.

Further, on the back surface of the solar cell module, etc.
An AC module called a MIC (Module Integrated Converter) that can install a small inverter that converts DC power generated by solar cells into AC power It is attracting attention as a solar power generator and an emergency power supply.

[0005] As disclosed in Japanese Patent Application Laid-Open No. 10-14111, the AC module is connected to a single-phase three-wire neutral line and one power line, and is connected to a system. In a solar power generation device using an AC module, in an emergency, DC power stored in a storage battery is converted into AC power by an emergency inverter and used.

[0006]

An AC module is connected to a building system via a distribution board or the like. in Japan's case,
Since the voltage of the grid in the building is 100V or 200V, AC
The module also needs to select 100V or 200V output depending on its connection. Therefore, the manufacturer of the AC module
When supplying to Japan, it is necessary to prepare two types of output, 100V and 200V, and if foreign countries are included, it is necessary to manufacture an AC module that can support various types of system voltage.

The present invention addresses the above problems individually or
The purpose of the present invention is to solve the problem collectively, and it is an object of the present invention to enable a power conversion device to easily cope with various types of system voltages.

Another object is to set the output voltage of the power converter according to the system voltage.

It is another object of the present invention to facilitate movement and installation of the power converter in an emergency or the like.

[0010]

The present invention has the following configuration as one means for achieving the above object.

[0011] A power converter according to the present invention is a power converter linked to a power system, comprising: a conversion circuit for converting DC power to AC power; and a transformer circuit for converting output power of the conversion circuit. A switch that opens and closes the transformer circuit and the power system, and controls the operation of the conversion circuit and / or the transformer circuit, and the opening and closing of the switch based on a system voltage and a connection state of the power system. And control means.

Preferably, the apparatus further comprises a plurality of connection means for connecting the switch and the power system, and the control means controls the plurality of connection means based on a detected system voltage of the power system. It is characterized by activating one.

[0013] Further, there is provided a power conversion device interconnected to a power system, wherein the conversion circuit converts DC power into AC power.
A transformer circuit for transforming the output power of the converter circuit, a switch for opening and closing the transformer circuit and the power system, and a type of connection means used for connection to the power system; Alternatively, a power conversion device comprising: a control unit that controls the operation of the transformer circuit and the switching of the switch.

[0014] Further, there is provided a power conversion device interconnected to a power system, wherein the conversion circuit converts DC power into AC power.
A switch for opening and closing the conversion circuit and the power system, and a control unit for controlling the operation of the conversion circuit and the opening and closing of the switch based on a type of connection unit used for connection to the power system. And characterized in that:

A power generator according to the present invention uses the above-mentioned power converter.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a photovoltaic power generator according to an embodiment of the present invention will be described in detail with reference to the drawings.

[Solar Cell] The solar cell used in the embodiment is not particularly limited. Examples of a silicon semiconductor photovoltaic element include a monocrystalline silicon solar cell, a polycrystalline silicon solar cell, and an amorphous silicon solar cell. As the photovoltaic element, a group III-V compound solar cell, a group II-VI compound solar cell and a group I-III-VI compound solar cell can be used.

A desired number of solar cells are connected in series and parallel, and are arranged between a surface protection member such as glass or a weather-resistant film and a back surface reinforcement such as a moisture-proof protection sheet or a metal steel plate, and are fixed by a filler. Thus, a solar cell module is formed.

The solar cell module often has a terminal box for taking out electric power on the non-light-receiving surface, or an output cable structure in which an output cable having a waterproof connector is attached at the end thereof. A plurality of solar cell modules can be connected to form a solar cell array by connecting terminal boxes using output cables or connecting waterproof connectors.

In the present embodiment, an inverter for converting DC power output from a solar cell module into AC power is mounted on the back surface of the solar cell module or electrically and / or mechanically attached to a terminal box. Connected AC
It can also be applied to modules.

[Booster circuit] A booster circuit is a circuit that boosts the voltage of DC power output from a DC power supply such as a solar cell to a voltage required by an inverter circuit. A parallel chopper circuit or the like can be used.

FIG. 1 is a diagram showing an example of a boost chopper circuit.

Turning on / off the switching element 2 charges the capacitor 5 via the diode 4 with the sum of the input voltage Vi and the voltage induced in the coil 3, thereby obtaining an output voltage Vo higher than the input voltage Vi. . An IGBT, a MOSFET, or the like is used for the switching element 2.

The output voltage Vo of the booster circuit is determined according to the on / off ratio (duty ratio) of the gate signal S input to the switching element 2 from the control circuit 104. Control circuit 10
Reference numeral 4 controls the duty ratio of the gate signal S according to the boost target voltage determined based on the output voltage / current of the solar cell, the output voltage of the inverter, and the like.

[Inverter Circuit] As the inverter circuit, a voltage type inverter using an IGBT or MOSFET as a switching element is preferable. The control circuit 104 supplies a gate signal to the inverter circuit to drive the plurality of switching elements to obtain a desired output voltage and current. The inverter circuit is controlled so as to perform a current control operation in an interconnected operation mode connected to the system, and to perform a voltage / frequency control operation in an independent operation mode not connected to the system. These operations and controls are known,
For example, it is disclosed in JP-A-58-69470, but is not limited to this.

[Control Circuit] FIG. 2 is a block diagram showing a configuration example of the control circuit 104.

In FIG. 2, a CPU 702 controls start / stop and an operation mode of the inverter. In the interconnection operation mode, the CPU 702 receives the output voltage and the current of the solar cell and generates a target voltage command value and a current command value.
Further, in the self-sustaining operation mode, when the output voltage of the monitored solar cell becomes equal to or lower than a predetermined value, a gate block signal is output to stop the inverter. However, in the case of a power generator with a storage battery, without stopping the inverter,
A switch is switched to convert DC power obtained from the storage battery into AC power. In this case, the operation of the inverter is continued until the output voltage of the storage battery becomes equal to or lower than the predetermined voltage.

The PWM waveform control unit 703 receives a voltage reference value or a current reference value, performs a so-called feedback control so that the respective reference values match the output voltage or the current, and supplies a gate to the switching element of the inverter circuit. Generate a signal. Such a circuit is described, for example, in Kyoritsu Shuppan Co., Ltd., "Power Electronics" by Tagao Hirasata. In the present embodiment, PI (proportional
-Integration) Use a triangular wave comparison type PWM waveform generation circuit using a control system.

The frequency / voltage reference generator 704 has a constant amplitude
An oscillation circuit that generates a sine wave of a constant frequency can be appropriately selected from known devices such as a Wien bridge circuit and used. In the present embodiment, a sine wave oscillator is configured by an operational amplifier and generates a voltage reference signal.

The current reference generator 705 generates a sine wave (current reference signal) having an amplitude corresponding to the current command value received from the CPU 702 and having a phase substantially coincident with the system voltage. Such a control circuit is disclosed in, for example, JP-A-58-69470, and includes a multiplier, a transformer for inputting a system voltage, and the like. In the present embodiment, a current reference signal is generated using a multiplier and a transformer.

The mode switch 706 selectively supplies a current reference signal to the PWM waveform control section 703 in the interconnection operation mode represented by the mode switching signal output from the CPU 702 and a voltage reference signal in the independent operation mode. The mode switch 70
For 6, a relay or an analog switch can be used. In this embodiment, a small relay is used.

The switching control unit 707 outputs a gate signal to the booster circuit based on the target voltage command value output from the CPU 702. Therefore, the output voltage Vo of the booster circuit is controlled to be the target voltage. In the present embodiment, the switching control unit 707 is configured using a comparator and a multiplier.

As described above, the control circuit 104 preferably has a voltage / frequency reference used in the self-sustained operation mode and a current reference used in the interconnected operation mode, and can preferably switch between them. Also, the control circuit 104
May be operated from the outside via a communication line or a communication path, or the control circuit 104 itself may be arranged outside the inverter to control a plurality of inverters collectively.

The target value of the output voltage is determined in advance by a control circuit.
It may be set to 104, or may be set according to the use condition of the inverter using a dip switch or the like.

[Switch] An electromagnetic switch or a breaker is used for a switch installed in a distribution board disposed between the inverter and the output terminal of the photovoltaic power generator and between the output terminal and the system. Etc. are available. In the case of an electromagnetic switch, the switching operation is performed according to a signal input from the control circuit 104, for example.

[Voltage / Current Detector] The voltage / current detector is not particularly limited, but a shunt resistor or a current transformer is used as the current detector. Then, the terminal voltage of the shunt resistor and the output voltage of the current transformer are A / D converted and input to the control circuit 104. Further, a transformer or a resistive voltage divider is used as the voltage detector. Then, the output voltage of the transformer or the resistor voltage divider is A / D converted and input to the control circuit 104. The voltage / current detector and the main circuit may be either insulated or non-insulated.

[0037]

First Embodiment FIG. 3 is a block diagram showing a configuration example of a photovoltaic power generator according to a first embodiment.

In FIG. 3, the DC power generated by the solar cell module 101 has a booster circuit 102, an inverter circuit 103, a control circuit 104, a transformer circuit 105, a switch 108, an output connector 106, and a system voltage detector 111. It is converted to AC power by the inverter. The output of the inverter 107 is connected to the system 110 via the distribution board 109.

As the solar cell module 101, a solar cell module PV-MR140 manufactured by Mitsubishi Electric (rated output 140W, 1
9.6V, 7.15A) is used. Although the solar cell module may be used alone, a solar cell array may be configured by connecting a plurality of solar cell modules. The number of series-parallel solar cell arrays may be appropriately set according to the allowable input voltage of the inverter 107 and the allowable voltage and current of the wiring of the DC circuit.

The system 110 is not limited to a commercial power system, but may be a system such as a private AC power generation facility in a factory or the like.

When the inverter 107 is connected to the grid,
The system voltage is detected by the system voltage detector 111, and a signal indicating the system voltage is sent to the control circuit 104. Control circuit 104
When the system is not connected to the connector 106 and the detected value of the system voltage is almost 0 V, the switch 108 is opened.

When the system is connected to the connector 106 and a system voltage of 200 V is detected, the control circuit 104
After a signal is sent to the relay 201 of the transformer circuit 105 shown in detail in FIG. 4 to connect the two secondary windings of the transformer 203 in series, the switch 108 is closed at an appropriate timing. As a result, inverter 107 operates in the interconnection operation mode in which 200 V AC power is output.

On the other hand, when a system voltage of 100 V is detected,
The control circuit 104 sends a signal to the relay 201,
After the two secondary windings are connected in parallel, the switch 108 is closed at an appropriate timing. As a result, inverter 107 operates in the interconnection operation mode that outputs 100 V AC power.

That is, since the control circuit 104 switches the setting of the transformer circuit 105 according to the detected system voltage, the inverter 107 operates in the interconnection operation mode in which 200 V or 100 V AC power is output according to the system voltage. Operate. It should be noted that the control circuit 104 controls the transformation circuit 105 according to the detected system voltage.
And the set value of the detection voltage of the overvoltage protection circuit (not shown) is also switched.

Also, although the transformer utilization efficiency decreases,
Using a transformer 203 having a 100 V tap, when the system voltage is 200 V, power is taken out from both ends of the secondary winding, and 10
In the case of 0V, a configuration in which power is taken out from a 100V tap may be used.

As described above, the inverter 107 according to the first embodiment is
Detects the system voltage and outputs AC power of a voltage corresponding to the system voltage, so that it is not necessary to prepare a plurality of types of inverters corresponding to the system voltage.

[0047]

Second Embodiment FIG. 5 is a block diagram showing a configuration example of a photovoltaic power generator of a second embodiment. Inverter 107 of the second embodiment
Has an output cable with a plug 311 for 200V at its tip and an output cable with a plug 312 for 100V. Plugs 311 and 312 are 200V
And 100V wall outlets 314 and 313.

FIG. 6 is a block diagram showing a configuration example of the transformer circuit 105. Relays 204 and 205 for opening and closing lines connected to plugs 311 and 312 are added to the configuration of the transformer circuit 105 of the first embodiment shown in FIG. The contacts of the relays 204 and 205 also serve as the switch 108 of the first embodiment.

The control circuit 104 opens both the relays 204 and 205 when the detected value of the voltage detector 111 for detecting the voltage of each of the lines of the plugs 311 and 312 is substantially 0V.

Then, when the plug 311 is connected to the corresponding wall outlet 314 and a system voltage of 200 V is detected,
The control circuit 104 sends a signal to the relay 201,
After the two secondary windings are connected in series, a signal is sent to the relay 204 at an appropriate timing to close the line connected to the plug 311. As a result, inverter 107
It operates in the interconnection operation mode that outputs V AC power.

On the other hand, the wall outlet 3 corresponding to the plug 312
13 and when a 100 V system voltage is detected, the control circuit 104 sends a signal to the relay 201, and after connecting the two secondary windings of the transformer 203 in parallel, the relay circuit A signal is sent to 205 to close the line connected to plug 312. As a result, the inverter 107
It operates in the interconnection operation mode in which the AC power is output.

The control circuit 104 drives one of the relays 204 or 205 to close the line, and does not drive the other relay.

The control circuit 104 constantly monitors the current flowing through the line by the current detector 112, and immediately stops driving the relays 204 and 205 when the current flowing through the line becomes equal to or less than a predetermined value. Open. This is because if the plug 311 or 312 is disconnected from the outlet while the inverter 107 is operating, there is a risk of an accident such as an electric shock.

Alternatively, in the case of a grid-connected inverter, for example, the voltage detector 111 detects an abnormality in the line voltage and releases the drive of the relays 204 and 205 to open the lines. The power failure detection function by the protection device described in the "operation guideline" works and can be safely stopped.

These set values and set times are set arbitrarily according to the system to which the line is connected.

In order to prevent a short circuit when the plugs 311 and 312 are connected to the wall outlet at the same time, and to prevent an accident such as electric shock due to an unplugged plug, the voltage detector 111 and the current detector 112 are connected to the main circuit. Must be insulated from

When the plugs 311 and 312 are connected to the wall outlet at the same time, the control circuit 104 preferentially sets the 200V output, but of course may set the 100V output.

Further, although not shown in FIG.
7 may be provided with an output outlet for independent operation. In that case, the control circuit 104 that has detected the power failure outputs a gate-off signal to the booster circuit 102 and the inverter circuit 103, and releases the drive of the relays 204 and 205 to disconnect the inverter 107 from the system 110. Thereafter, the inverter circuit 103 is switched to the independent operation mode, and the gate-off signal is released. As a result, AC power can be obtained from the output outlet, so that even if a power failure occurs due to a disaster or the like, the photovoltaic power generator (at least the inverter 107)
Can be installed at any location to supply AC power to various loads.

As described above, the inverter 107 of the second embodiment is used.
As in the first embodiment, since the system voltage is detected and the AC power of a voltage corresponding to the system voltage is output, there is no need to prepare a plurality of types of inverters corresponding to the system voltage. Further, it can be easily connected to the system 110 via the plug 311 or 312 to perform the interconnection operation. In an emergency, it can be installed at an arbitrary location and effectively used as an emergency power supply.

FIG. 5 also shows two plugs 311 and 312
Although the example which is connected was shown, similarly to the first embodiment,
An output connector 106 may be provided at the output end of the inverter 107 so that only a cable having a required plug at its end can be connected. In this way, two plugs 31
Since it is not necessary to detect the voltage and current for each line connected to 1 and 312, only one set of the voltage detector 111 and the current detector 112 is required. Furthermore, the relay 20 of the transformation circuit 105
Either 4 or 205 becomes unnecessary.

[0061]

Third Embodiment The inverter 107 of the third embodiment has, at its output end, an output connector (receptacle) 801 into which a plug 802 is inserted as shown in FIG. The shape of plug 802 is
The plug 802 is distinguished from A, B, B3, BF, C, O, and SE, and is used in a region where the photovoltaic power generation device is used or in a shape suitable for a voltage desired by the user. Although details will be described later, the inverter 107 outputs a voltage according to the shape of the plug 802.

The bottom of the receptacle 801 has an opening 808 through which the projection 806 of the plug 802 can pass. The projection 806 that passes through the opening 808 turns on the switch 807. When switch 807 is on, control unit 104 determines that plug 802 for, for example, 200 V is connected.

The power electrodes 805 and 804 can be fitted together, and when the plug 802 is inserted into the receptacle 801,
Inverter 107 is connected to system 110 via cable 803.

FIG. 8 is a block diagram showing a configuration example of the photovoltaic power generator of the third embodiment.

The plug 802 connected to the receptacle 801
In the case of 100 V, the control circuit 104 controls the output voltage of the booster circuit 102 to a first target value (for example, 160 V), and sets the inverter circuit 103 to a 100 V output interconnection operation mode. When the plug 802 is for 200 V, the control circuit 104 controls the output voltage of the booster circuit 102 to a second target voltage (for example, 320 V), and sets the inverter circuit 103 to a 200 V output interconnected operation mode.

Although the detailed description is omitted, when changing the voltage, the inductance of the inductor 5 and the interconnection reactor (not shown) shown in FIG. 1 is changed as necessary. The operation of the switch 108 is the same as in the first embodiment. Although not shown in FIG. 8, the control circuit 104 includes a voltage detector and a current detector, and when the voltage indicated by the plug 802 is different from the voltage of the system 110 or when the plug 312 is disconnected, the control circuit 104
8 is opened. Needless to say, the voltage change circuit 105 may be used for changing the voltage as in the first embodiment.

Further, the inverter 107 shown in FIG. 8 includes a storage battery 617 for supplying DC power at night or when the solar cell module 101 cannot be connected, a charge / discharge control circuit 618 for controlling the charge / discharge of the storage battery 617, and And a switch 616 for opening and closing the connection between the solar cell module 101 and the storage battery 617. The storage battery 617 may be arranged inside the inverter 107 or outside. The control circuit 104 operates in a self-sustaining operation such as at night or when sunlight is weak.
When the output of 101 does not exceed the predetermined voltage, when the output of solar cell module 101 is detected to be low, switch 616 is closed and charge / discharge control circuit 618 supplies the power of storage battery 617.

As described above, according to the inverter of the fourth embodiment, the system voltage can be known from the shape of the plug connected to the inverter 107, and AC power of a voltage corresponding to the system voltage is output. There is no need to prepare multiple types of inverters according to the voltage. Further, similarly to the second embodiment, it is possible to easily connect to the system 110 via the plug 311 or 312 and perform the interconnection operation. In an emergency, it can be installed at an arbitrary place together with the storage battery 617 and can be effectively used as an emergency power supply.

The following effects can be expected by using the solar power generation device of the above-described embodiment. (1) The inverter according to the embodiment detects the system voltage and outputs AC power of an appropriate voltage, so that the system interconnection can be easily performed. (2) The inverter of the embodiment, for example, according to the system voltage
Since 100V or 200V AC power is output, there is no need to manufacture and prepare a plurality of inverters according to the system voltage to be interconnected. (3) The inverter according to the embodiment is normally used in connection with a system during normal times, and can be moved to an arbitrary place in an emergency, so that it can be effectively used as an emergency power supply. (4) The inverter of the embodiment does not perform special connection,
It can be easily connected to a wall outlet of a building, etc., and can easily connect to the grid and supply power in an emergency. Furthermore, even when the plug is unplugged from the wall outlet or when improper connection is made, an operation can be performed in consideration of safety.

In the above description, when the system voltage is 100 V and 20 V
Although the case of 0 V has been described, it is also possible to cope with various system voltages in various regions.

Although not described in detail, when the photovoltaic power generator or the inverter according to the embodiment is used as an emergency power supply, when the output switch of the inverter does not close due to the absence of system voltage or the like. There is. In consideration of such a case, it is desirable to provide a switch for switching the operation of the control circuit 104 to the emergency power supply operation mode.
With this switch, operation modes such as “normal operation”, “emergency 100V output”, and “emergency 200V output” can be set.

Further, in the normal state, the output switch of the inverter is opened when the output current becomes equal to or less than a predetermined value in consideration of the case where the plug is disconnected from the wall outlet. In consideration of this, measures such as lowering the output current value for opening the output switch are taken.

[0073]

As described above, according to the present invention,
The power converter can be easily adapted to various system voltages.

The output voltage of the power converter can be set according to the system voltage.

Further, movement and installation of the power converter in an emergency or the like can be facilitated.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a boost chopper circuit;

FIG. 2 is a block diagram illustrating a configuration example of a control circuit.

FIG. 3 is a block diagram illustrating a configuration example of a solar power generation device according to a first embodiment;

FIG. 4 is a block diagram illustrating a detailed configuration example of a transformer circuit according to the first embodiment;

FIG. 5 is a block diagram illustrating a configuration example of a photovoltaic power generator according to a second embodiment;

FIG. 6 is a block diagram illustrating a detailed configuration example of a transformer circuit according to a second embodiment;

FIG. 7 is a diagram illustrating an output connector (receptacle) at an output end of the inverter according to the third embodiment;

FIG. 8 is a block diagram illustrating a configuration example of a photovoltaic power generator according to a third embodiment.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F051 JA17 KA02 KA03 KA05 5G066 HA01 HB05 LA08 5H007 BB07 CC12 CC23 CC33 CC34 DB07 DC02 DC05 EA02

Claims (13)

[Claims] 1. A power conversion device interconnected to a power system, comprising: a conversion circuit for converting DC power to AC power; a voltage conversion circuit for converting output power of the conversion circuit; A switch for opening and closing a system, based on a system voltage and a connection state of the power system, an operation of the conversion circuit and / or the transformer circuit, and
Control means for controlling opening and closing of the switch. 2. The power converter according to claim 1, wherein the control circuit controls an operation of the conversion circuit based on a detected system voltage of the power system. 3. The power converter according to claim 1, wherein the control circuit sets a transformation ratio of the transformation circuit based on a detected system voltage of the power system. 4. A power supply system comprising: a plurality of connection means for connecting the switch and the power system; wherein the control means is configured to detect one of the plurality of connection means based on a detected system voltage of the power system. 4. The power conversion device according to claim 1, wherein one of the power conversion devices is activated. 5. A booster circuit for boosting a DC voltage supplied to the conversion circuit, wherein the control means controls a DC voltage output from the booster circuit based on a system voltage of the power system. 5. The power converter according to claim 1, wherein: 6. A power converter connected to a power system, comprising: a conversion circuit for converting DC power into AC power; a voltage conversion circuit for converting output power of the conversion circuit; A switch for opening and closing a system, and a control unit for controlling the operation of the conversion circuit and / or the transformer circuit, and controlling the opening and closing of the switch based on a type of connection unit used for connection to the power system. And a power converter. 7. A power conversion device interconnected to a power system, comprising: a conversion circuit for converting DC power into AC power; a switch for opening and closing the conversion circuit and the power system; And a control means for controlling the operation of the conversion circuit and the opening and closing of the switch based on the type of connection means used for the connection. 8. The power conversion device according to claim 6, wherein the control circuit detects a type of the connection unit and controls an operation of the conversion circuit based on a result of the detection. apparatus. 9. A booster circuit for boosting a DC voltage supplied to the conversion circuit, wherein the control means controls the DC voltage output from the booster circuit based on a type of the connection means. 9. The power conversion device according to claim 6, wherein: 10. The power converter according to claim 6, wherein the control circuit detects a type of the connection unit, and sets a transformation ratio of the transformation circuit based on a result of the detection. 11. A power generator using the power converter according to any one of claims 1 to 10. 12. The power generator according to claim 11, further comprising a solar cell. 13. The power generator according to claim 11, further comprising a storage battery charge / discharge control circuit.