JP2004297880A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a starting characteristic of a power converter for use in a single cell converter. <P>SOLUTION: The power converter comprises: voltage driving type switching elements 33, 34 that boost DC voltages outputted from a solar battery cell; a drive signal generation part 113 that generates drive signals of the switching elements; and a control power supply 102 that boosts the DC voltages outputted from the solar battery cell and feeds powers to the switching elements and the drive signal generation part. The power converter determines whether a voltage of the drive signal reaches a prescribed threshold or higher by comparing an output voltage of the control power supply 102 with a voltage of a reference voltage source 114 by a comparator 115, and controls the drive signal generation part 113 so as to generate a drive signal only when the output voltage of the control power supply 102 reaches the voltage of the reference voltage source 114 or higher. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power converter, and more particularly, to a power converter that boosts a DC voltage output from a solar cell and a solar power generation system including the power converter.
[0002]
[Prior art]
In recent years, problems such as global warming due to emission of carbon dioxide and the like accompanying the use of fossil fuels, nuclear power plant accidents and radioactive contamination by radioactive waste have become serious, and interest in the global environment and energy has been increasing. Under such circumstances, photovoltaic power generation using sunlight as an inexhaustible and clean energy source has been put to practical use all over the world.
[0003]
As a form of photovoltaic power generation using a solar cell, there are various forms depending on the output scale from several W to several thousand kW. As a typical system using a solar cell, there is a system that converts DC power generated by the solar cell into AC power (orthogonal conversion) by an inverter or the like and supplies the AC power to a load of a customer or a commercial power system.
[0004]
FIG. 9 is a diagram showing an appearance of a general home-use solar power generation system, and FIG. 10 is a schematic block diagram of the solar power generation system of FIG.
[0005]
In the figure, reference numeral 75 denotes a solar cell module, which is configured so that a plurality of solar cells having an output voltage of several volts are connected in series so that the output voltage becomes about 20 volts. Furthermore, a plurality of solar cell modules 75 are connected in series to form a solar cell string 76 capable of obtaining an output voltage of about 200 V, and connected to the system interconnection inverter 71 to construct a system interconnection system.
[0006]
As shown in FIG. 10, the grid interconnection inverter 71 is output from a DC / DC converter unit 72 that converts an output voltage from a solar cell whose voltage changes variously to a constant voltage, and output from the DC / DC converter unit 72. The DC / AC converter 73 converts the DC power into commercial AC power of a frequency and a voltage that can be connected to the system.
[0007]
FIG. 11 is a diagram illustrating an example of a configuration of the DC / DC converter unit 72 illustrated in FIG. The DC / DC converter section 72 has an FET as a switching element, and its drive circuit 1101 includes a control power supply section 1102, an oscillation section 1103, and an amplification section 1104. Is output, and this voltage is stepped down to generate a control power supply.
[0008]
While the rated output voltage of the solar cell string is 200 V, the drive voltage for driving the switching element and the control voltage in the inverter are at most about 3 to 15 V. Therefore, in such a configuration, since the voltage of the control power supply is generated from the sufficiently high output voltage of the solar cell, a sufficient voltage value can be easily obtained.
[0009]
However, such a configuration using a solar cell string in which a large number of solar cells are connected in series has the following problems.
[0010]
For example, when sunlight is blocked by an obstacle or the like and shade occurs, cells in the shaded portion do not generate power. For a cell that does not generate power, the entire voltage of the other solar cells connected in series is applied in the opposite direction to the photovoltaic voltage of the solar cell or element via the load connected to the solar cell module, and a reverse current flows. Generates heat. To prevent this, there is a method of providing a bypass diode for each cell, but this increases the cost of the module and the system.
[0011]
Further, in order to connect the cells in series, it is necessary to provide a non-power generation region that is not used for power generation between the cells, so it is difficult to increase the area power generation efficiency of the solar cell module.
[0012]
Further, for example, when a solar cell using a conductive substrate as a negative electrode is used, a pinhole is formed in a sealing material between the conductive substrate of the solar cell connected in series and the outer conductor of the solar cell module. Occurs, and when rainwater enters the solar cell, the solar cell and the outer conductor of the solar cell module are brought into conduction through the rainwater.
[0013]
In such a state, a leakage current flows to the adjacent solar cell module via the outer conductor portion of the solar cell module, and this current may corrode the outer conductor portion of the solar cell module.
[0014]
In order to address these problems, the inventors of the present application have proposed solar power generation systems using a single cell converter (Japanese Patent Application Nos. 2002-207192 and 2002-231804).
[0015]
This is not a configuration in which outputs from a large number of solar cells connected in series are connected to an inverter as in the conventional solar cell string 76, but a DC / DC converter for each single cell or a small number of cells connected in series. Are provided to form a single-cell converter, and the outputs of the plurality of single-cell converters are connected to an inverter.
[0016]
According to the photovoltaic power generation system having such a configuration, the above problem can be solved and the following effects can be obtained.
[0017]
The capacity of the solar cell module can be changed simply by increasing or decreasing the number of single-cell converters, and a small-capacity solar power generation system can be easily configured.
[0018]
The ground voltage of the solar cell can be reduced, and as a result, the coating of the solar cell element can be thinned to reduce the manufacturing cost.
[0019]
[Problems to be solved by the invention]
However, in a photovoltaic power generation system using a single-cell converter, if a DC / DC converter is configured to include a booster circuit using a switching element such as an FET, a low drive voltage is supplied to the switching element before the system starts. In some cases, the startup characteristics may be degraded.
[0020]
This phenomenon will be described in more detail. When the switching FET of the DC / DC converter is driven by open-loop control, the output voltage of the solar cell is boosted to generate a driving voltage for the switching FET. In this case, when a drive voltage that is low and not boosted to a sufficient voltage is supplied to the FET at the time of startup or the like and the output voltage from the solar cell is low, the conversion operation is performed in a state where the loss due to the ON resistance of the FET is very large. .
[0021]
For this reason, when the output from the solar cell is low without sufficient solar radiation such as in the early morning, the loss due to the ON resistance of the FET increases, and the output voltage of the DC / DC converter may be boosted to a desired voltage. I can no longer do it. That is, it takes time for the output voltage of the DC / DC converter to reach a desired voltage, and the starting characteristics of the solar cell deteriorate.
[0022]
This phenomenon will be described in more detail with reference to the block diagram of the DC / DC converter shown in FIG.
[0023]
In FIG. 2, 32 is an input capacitor, 33 and 34 are switching elements such as FETs, 15 is a transformer, 36 is a rectifier circuit, 37 is a smoothing circuit, and 101 is a drive circuit that supplies a drive voltage to the gate of the switching element. . The drive circuit 101 mainly includes a control power supply 102, an oscillator 103, and an amplifier 104.
[0024]
<Control power supply 102>
The control power supply 102 receives the power output from the solar cell in parallel with the main circuit of the DC / DC converter 2, boosts a low voltage output from the solar cell, and generates a voltage of about 5 V for driving the switching element. Generate.
[0025]
The control power supply 102 includes a boost chopper circuit including an input smoothing capacitor, a smoothing coil, a chopper switch, a chopper diode, and an output smoothing capacitor. The boost ratio of the boost chopper circuit is determined by the duty of the drive pulse supplied to the chopper switch, and the output voltage can be adjusted to 5 V by monitoring the chopper output voltage and adjusting the duty.
[0026]
However, the boost ratio can be increased by increasing the duty ON time ratio, but the inductance value and resistance value of the input inductor, the drive signal becomes dull, and the collector-emitter voltage (drain-source voltage) when the chopper switch is turned on. The step-up ratio has a practical limit due to the inter-voltage, etc., and a practical step-up ratio is up to about six times.
[0027]
<Oscillator 103>
The oscillating unit 103 outputs a square wave pulse having a driving frequency for driving the switching elements 33 and 34 of the DC / DC converter 2 by the power supply of 5 V boosted by the control power supply 102. The switching frequency of the oscillation unit 103 in this example was set to 70 kHz.
[0028]
<Amplifier 104>
The amplification unit 104 current-amplifies the square wave pulse generated by the oscillation unit 103. This is to supply a sufficiently drivable current to the switching elements 33 and 34.
[0029]
For example, when the switching elements 33 and 34 are configured by FETs, it is necessary to quickly charge the input parasitic capacitance to reduce switching loss, and for that purpose, a high current supply capability is required.
[0030]
As a power source for driving the amplifying unit 104, an output of the control power source 102 is input in parallel with the oscillation unit 103.
[0031]
When the output of the oscillation unit 103 has a sufficient driving capability, the amplification unit 104 is not necessary.
[0032]
<Operation of DC / DC converter>
In the driving circuit 101 having such a configuration, the output voltage from the solar cell gradually rises when sunlight hits the solar cell, and when the output voltage becomes about 0.6 V to about 0.7 V, the boost voltage which is a control power supply is increased. The chopper circuit starts operating, and the drive voltage is supplied to the FET.
[0033]
Here, it is assumed that the relationship between the gate voltages of the FETs 33 and 34 used as the switching elements and the ON resistance is the characteristic shown in the graph of FIG. Generally, as shown in the graph of FIG. 6, when the gate voltage is low, the ON resistance (drain-source resistance) is high, and the FET is driven when the output voltage of the control power supply has not reached the threshold voltage. In such a case, conduction occurs with a large loss caused by the FET.
[0034]
In particular, as shown in FIG. 6, in an FET having a minimum gate threshold voltage of 1.0 V and a maximum value of 3.0 V, when the gate voltage falls below the maximum value of 3.0 V, the ON resistance tends to increase further. There is.
[0035]
For this reason, the power loss due to the FET having a sufficiently small level is usually not negligible, and the power output from the DC / DC converter is
[Input power]-[FET power loss]-[Main circuit fixed loss such as transformer core loss]
When the power output from the solar cell is small in the early morning or the like, the power output from the DC / DC converter is very small.
[0036]
Furthermore, when the switching element ON time ratio at the time of startup is high, especially in fixed duty control or the like, the relationship between the output voltage and the input voltage becomes constant, so that the input voltage does not rise easily. As a result, even if the amount of solar radiation increases, the gate voltage of the FET is low, → the ON resistance of the FET is high and the loss is large, → the output voltage does not rise easily, → the input voltage does not rise, → the gate voltage of the FET rises. A low loop occurs.
[0037]
FIG. 7 is a graph showing the relationship between the amount of solar radiation and the output power of such a DC / DC converter. If the amount of solar radiation does not reach a certain level, the output power is extremely small and the starting characteristics are low. It is shown.
[0038]
The present invention has been made in view of the above situation, and has as its object to improve the starting characteristics of a power converter used in a single-cell converter.
[0039]
[Means for Solving the Problems]
A power converter according to one embodiment of the present invention that achieves the above object is a power converter that boosts a DC voltage output from a solar cell,
A voltage-driven switching element,
A drive signal generation unit that generates a drive signal for the switching element;
A control power supply unit that boosts a DC voltage output from the solar cell and supplies power to the switching element and the drive signal generation unit,
Determining means for controlling to generate the drive signal only when the voltage of the drive signal is equal to or higher than a predetermined threshold.
[0040]
That is, in the present invention, in order to boost the DC voltage output from the solar cell, a voltage-driven switching element, a drive signal generating unit that generates a drive signal for the switching element, and a DC output from the solar cell. And a control power supply unit that boosts the voltage and supplies power to the switching element and the drive signal generation unit. In the power converter, the drive signal is generated only when the voltage of the drive signal is equal to or higher than a predetermined threshold. Control.
[0041]
With this configuration, when the voltage generated from the solar battery cell is lower than the voltage required for the voltage of the drive signal to be equal to or higher than the predetermined threshold, the drive signal is not output, and the switching element is appropriately switched. It can be driven in a state, for example, a state where the ON resistance is always small.
[0042]
Therefore, it is possible to improve the startup characteristics of the power converter in a configuration in which the voltage input to the power converter is low, such as a single cell converter in which a power converter is provided for each single cell or a small number of cells connected in series. it can.
[0043]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a power converter according to the present invention and a photovoltaic power generation system using the power converter will be described in detail with reference to the drawings. In all the drawings, the same components are denoted by the same reference numerals.
[0044]
First, the overall configuration of a photovoltaic power generation system according to the present invention and its components will be described.
[0045]
[Configuration of solar power generation system]
FIG. 1 is a block diagram showing a configuration of a photovoltaic power generation system including a DC / DC converter as a power converter according to the present invention.
[0046]
In FIG. 1, 1 is a solar cell, 2 is a DC / DC converter, 3 is an inverter, and 4 is a commercial power system. In the configuration according to the present invention, a plurality of single cell converters each including a solar cell 1 and a DC / DC converter 2 are connected in parallel, the output of which is input to the inverter 3, and the commercial AC power output from the inverter 3 is A system interconnection system that flows backward to the power system 4 is configured.
[0047]
<Solar cell 1>
The solar cell 1 is installed outdoors, such as a roof, so that sunlight is radiated without being interrupted. The number of solar cells connected in series is limited to one or more (for example, less than four), and the output voltage is reduced. Is configured to have a low voltage. Further, it is preferable to use a large current solar cell having an output current of 10 A or more.
[0048]
Various solar cell elements such as an amorphous silicon type, a polycrystalline silicon type, and a crystalline silicon type can be used for the solar cell.
[0049]
In this configuration, a stacked solar cell in which three layers of amorphous silicon were stacked was used as the solar cell 1. Its characteristics are
Rated solar radiation = 1 kW / m ² : Ambient temperature 25 ° C
Short-circuit current Isc = 16.10 A
Open circuit voltage Voc = 1.8V
Maximum operating point current Ipm = 14.0A
Maximum operating point voltage Vpm = 1.4V
Maximum output power Pmax = 20W
It has become.
[0050]
<DC / DC converter 2>
An open-loop DC / DC converter 2 is provided for each solar cell 1 to boost the output of the solar cell 1 having a low voltage and a large current and convert the output to a high voltage and a small current. This aims to reduce power transmission loss in a long power transmission path up to the inverter 3 that is grounded indoors.
[0051]
Hereinafter, the configuration of the DC / DC converter 2 will be described with reference to FIG. In FIG. 1, 32 is an input capacitor, 33 and 34 are switching elements such as FETs, 15 is a transformer, 36 is a rectifier circuit, 37 is a smoothing circuit, and 46 is a drive circuit for supplying a drive voltage to the gate of the switching element. .
[0052]
The drive circuit 46 supplies two gate drive signals having phases opposite to each other to the switching elements 33 and 34 constituting the push-pull switching circuit. The duty ratio of the gate drive signal (rectangular wave) is fixed.
[0053]
The gate drive circuit 46 is a control power supply that boosts the output of the solar cell 1 to supply operation power for the entire gate drive circuit, and a determination unit that determines whether the drive voltage to the switching element 33 is equal to or higher than a predetermined threshold. An oscillator for generating a drive signal for the switching element, and an amplifier for amplifying the output of the oscillator when the oscillation element cannot directly drive the switching element.
[0054]
The judging means is composed of a comparator and a reference voltage source. The comparator determines the output voltage of the solar cell 1 and the control power supply in order to judge whether the drive voltage to the switching element 33 is equal to or higher than a predetermined threshold. One of the input voltage, the output voltage of the control power supply, the input voltage of the oscillating means, the input voltage of the amplifying means, and the like is used as one input, a reference voltage source for generating a predetermined voltage is used as the other input, and one input voltage is used as the other input. When the input voltage exceeds the input voltage, a signal for permitting the driving of the switching element is output. The signal for permitting the driving of the switching element is output to at least one of the control power supply, the oscillation unit, and the amplification unit.
[0055]
The predetermined threshold value in the determination means is set to a preferable value as appropriate according to the circuit configuration. However, a voltage equal to or higher than a threshold voltage at which the ON resistance of the switching element rapidly decreases becomes a drive signal from the drive circuit 46. It is sufficient that the voltage is such that it is output.
[0056]
Further, the determination means may be configured so that the output voltage of the solar cell is directly level-shifted by a constant voltage diode or the like and connected to at least one control input of a control power supply, an oscillation means, and an amplification means.
[0057]
The duty of the gate drive signal output from the drive circuit 46 is preferably 50%, which is the maximum duty of the push-pull switching circuit, because the conversion efficiency is high. The reason why the duty of the gate drive signal is fixed is to eliminate the feedback circuit and simplify the switching control circuit, thereby improving cost reduction and reliability. The switching frequency is set in the range of 20 kHz to several hundreds kHz due to a trade-off between power loss due to switching and miniaturization of the transformer.
[0058]
In addition, since the switching elements 33 and 34 have a low output voltage of the solar cell 1, it is preferable to use MOSFETs with low on-resistance. At present, MOSFETs, which are unipolar elements, are particularly excellent in terms of on-resistance.
[0059]
As the input capacitor 32, it is preferable to use an OS capacitor (manufactured by Sanyo Electric Co., Ltd.) having a small equivalent series resistance (ESR) and excellent in high frequency characteristics so that the power supply source can be regarded as a voltage source when viewed from the DC / DC converter 2. . In addition, a capacitor having a small ESR such as a multilayer ceramic capacitor or a tantalum electrolytic capacitor can be used. The input capacitor 32 allows the power supply source of the DC / DC converter 2 to be regarded as a voltage source, and the DC / DC converter 2 is what is called a voltage-type converter.
[0060]
As for the transformation ratio (turning ratio) of the transformer 15, when the operating voltage of the solar cell 1 is minimum, a DC voltage (for example, 150 V or more) necessary for the inverter 3 to output an AC voltage of 100 V is supplied to the inverter 3. Set to Note that the output voltage of the DC / DC converter 2 is a value obtained by multiplying the input voltage by the transformation ratio of the transformer 15 because the switching circuit is always operated at the maximum duty.
[0061]
The optimum operating point of the solar cell has a characteristic that the voltage becomes low when the temperature is high or the amount of solar radiation is small. In this configuration, the operation start voltage of the solar cell is set to about 1.0 V, and the output voltage can be increased to 150 V at that time.
1.0 (V): 150 (V)
The actual number of windings was 2T for the primary winding and 300T for the secondary winding.
[0062]
A rectifier circuit 36 for rectifying the high-frequency AC output of the transformer and a smoothing circuit 37 for smoothing are provided at the subsequent stage of the transformer 15. When the input capacitor of inverter 3, which is the output destination of converter 2, is sufficiently large, smoothing circuit 37 may not be provided.
[0063]
[Operation of DC / DC converter 2]
In the configuration shown in FIG. 1, low-voltage DC power is input from the solar cell 1 to the DC / DC converter 2. The voltage of the input DC power is boosted by a booster circuit including the gate drive circuit 46, the switching elements 33 and 34, and the transformer 15. The high-frequency AC power output from the secondary winding of the transformer 15 is rectified by the diode bridge 36, smoothed by the smoothing circuit 37 and converted to DC, and then supplied to the inverter 3.
[0064]
[Operation of inverter 3]
The control circuit 53 of the inverter 3 monitors the voltage and the current input from the DC / DC converter 2 by the input voltage detector 54 and the input current detector 55, and performs PWM control of the switching element of the inverter bridge 52. With this control, the output voltage and output current of the DC / DC converter 2 are controlled, and as a result, the operating point voltage and current of the solar cell 1 can be controlled. In other words, the control circuit 53 can effectively utilize the power generated by the solar cell 1 by performing the maximum power tracking control using the DC / DC converter 2 and the solar cell 1 together.
[0065]
The DC power output from the inverter bridge 52 is converted into AC power by the filter 58 including the inverter bridge 52 and the interconnection reactor, and supplied to the commercial power system 4. As a method of monitoring the input voltage and the input current of the inverter 3 and performing the PWM control of the inverter bridge 52, any of a number of publicly known and public methods can be used, and a detailed description thereof will be omitted.
[0066]
By such PWM control of the inverter 3, while extracting the maximum power from the solar cell 1 and the DC / DC converter 2, the AC power having the same current phase as the commercial power system 4 and the power factor of 1 is output, and the System can be configured.
[0067]
Hereinafter, some embodiments of the DC / DC converter 2 in the photovoltaic power generation system configured as described above will be described.
[0068]
Note that, as described above, the present invention is a power converter that boosts a DC voltage output from a solar cell, includes a voltage-driven switching element, and a drive signal generation unit that generates a drive signal for the switching element. A control power supply unit that boosts the DC voltage output from the solar cell and supplies power to the switching element and the drive signal generation unit, and only when the voltage of the drive signal is equal to or higher than a predetermined threshold value, The power converter includes a determination unit that controls generation of the power. The embodiments described below also have the following features.
[0069]
That is, the drive signal generation unit generates, for example, a pulse-shaped drive signal by open-loop control. The predetermined threshold is the maximum value of the gate threshold of the switching element. The determination means includes a reference voltage source and a comparator.
[0070]
<First embodiment>
FIG. 3 is a block diagram showing the configuration of the DC / DC converter according to the first embodiment of the present invention. The DC / DC converter according to the present embodiment includes an input capacitor 32, switching elements 33 and 34, a transformer 15, a rectifier circuit 36, a smoothing circuit 37, and a drive circuit 111. Is provided for determining that the output of the oscillating unit is stopped when is smaller than a predetermined threshold value.
[0071]
Note that the configuration other than the drive circuit 111 is substantially the same as that in FIG. 2, and a description thereof will not be repeated.
[0072]
In the drive circuit 111, 102 is a control power supply, 104 is an amplifying unit, 113 is an oscillating unit, 114 is a reference voltage source, 115 is a comparator, and 116 is an output permission signal input terminal provided in the oscillating unit. That is, in the present embodiment, the reference voltage source 114 and the comparator 115 constitute a determination unit, and the output is input to the oscillation unit 113.
[0073]
In this embodiment, the voltage of the reference voltage source 114 is set to 3 V, and the input voltage of the oscillation unit 113, that is, the output voltage of the control power supply 102 and the output voltage (3V) of the reference voltage source 114 are compared by the comparator 115. When the input voltage of 113 becomes 3 V or more, an output permission signal is sent to the oscillation unit 113.
[0074]
With the above configuration, the oscillation unit 113 does not output an output pulse when the output of the control power supply 102 is less than 3V. The condition under which the oscillation unit 113 sends a pulse to the amplification unit 104 is a state where 3 V or more is supplied to both the oscillation unit 103 and the amplification unit 104, and the voltage supplied to the gate of the FET is 3 V or more. As a result, the FET is always used in a state where the ON resistance is small, and the gate voltage of the FET is low, the ON resistance of the FET is high and the loss is large, and the output voltage does not easily rise as in the conventional example. The voltage also does not increase. → A loop of lowering the starting characteristic that the gate voltage of the FET is low does not occur.
[0075]
FIG. 8 is a graph showing the relationship between the amount of solar radiation and the output power of the DC / DC converter of the present embodiment. It can be seen that the startup characteristics are improved as compared with the graph of the conventional DC / DC converter shown in FIG.
[0076]
(Modification)
In the first embodiment, the output permission signal is sent to the oscillating unit 113 in accordance with the result of comparison between the voltage of the reference voltage source 114 and the output voltage of the control power supply 102 by the comparator 115. The output voltage is shifted in voltage level through a diode, a zener diode, a voltage dividing resistor, or the like, and is input to the output permission signal input terminal 116 instead of the output permission signal to control the operation of the oscillation unit 113. Is also good.
[0077]
In this case, the value of the output voltage of the control power supply 102 is decreased by a predetermined value or a predetermined ratio, and when the output voltage of the control power supply 102 becomes 3 V or more, the voltage supplied to the output permission signal input terminal 116 Is set to be equal to or higher than a threshold voltage indicating output permission.
[0078]
With this configuration, the startup characteristics of the DC / DC converter can be improved with a simple configuration that does not require a reference voltage source and a comparator.
[0079]
<Second embodiment>
Hereinafter, a second embodiment of the DC / DC converter according to the present invention will be described. In the following, description of the same parts as those in the first embodiment will be omitted, and the description will focus on the characteristic parts of the present embodiment.
[0080]
FIG. 4 is a block diagram showing a configuration of a DC / DC inverter according to a second embodiment of the present invention. The configuration of the drive circuit 121 is different from that of the first embodiment. In the present embodiment, a determination unit that stops the output of the amplification unit when the output voltage of the control power supply 102 is lower than a predetermined threshold is provided.
[0081]
In the drive circuit 121, 102 is a control power supply, 103 is an oscillating unit, 114 is a reference voltage source, 115 is a comparator, 118 is an amplifying unit, and 117 is an output permission signal input terminal provided in the amplifying unit. That is, in the present embodiment, the reference voltage source 114 and the comparator 115 constitute a determination unit, and the output is input to the amplification unit 118.
[0082]
In this embodiment, the voltage of the reference voltage source 114 is set to 3 V, and the input voltage of the oscillation unit 113, that is, the output voltage of the control power supply 102 and the output voltage (3V) of the reference voltage source 114 are compared by the comparator 115. When the input voltage of the input terminal 113 becomes 3 V or more, an output permission signal is transmitted to the drive unit 118.
[0083]
With the above configuration, the amplifier 118 does not output a drive signal when the output of the control power supply 102 is less than 3V. The condition in which the amplification unit 118 sends a gate pulse to the FET is such that 3 V or more is supplied to both the oscillation unit 103 and the amplification unit 104, and the voltage supplied to the gate of the FET is 3 V or more. As a result, the FET is always used in a state where the ON resistance is small, and the above-mentioned loop of deterioration of the starting characteristic does not occur.
[0084]
A graph showing the relationship between the amount of solar radiation and the output power of the DC / DC converter according to the present embodiment is the same as that of FIG. 8 described for the first embodiment, and the starting characteristics are improved.
[0085]
<Third embodiment>
Hereinafter, a third embodiment of the DC / DC converter according to the present invention will be described. In the following, description of the same parts as those in the first and second embodiments will be omitted, and the description will focus on the characteristic parts of the present embodiment.
[0086]
FIG. 5 is a block diagram showing the configuration of the third embodiment of the DC / DC converter according to the present invention. The configuration of the drive circuit 131 is different from the first and second embodiments. In the present embodiment, the determination unit is configured so that the control power supply 102 itself does not output the output voltage when the input voltage of the control power supply 102 is lower than the predetermined threshold.
[0087]
In the drive circuit 121, reference numeral 102 denotes a control power supply, 103 denotes an oscillation unit, 104 denotes an amplification unit, 114 denotes a reference voltage source, 115 denotes a comparator, and 119 denotes an output permission signal input terminal provided in the control power supply. That is, in the present embodiment, the reference voltage source 114 and the comparator 115 constitute a determination unit, and the output is input to the control power supply 102.
[0088]
In the present embodiment, as the voltage of the reference voltage source 114, the voltage output from the control power supply 102 is set to a value of the input voltage (output voltage from the solar cell) at which the voltage becomes a sufficient value, for example, 3V. The comparator 115 compares the voltage output from the solar cell with the output voltage of the reference voltage source 115. When the voltage output from the solar cell becomes equal to or higher than the output voltage of the reference voltage source 115, the control power supply 102 The output permission signal is transmitted.
[0089]
With the above configuration, the same effects as those of the first and second embodiments can be obtained.
[0090]
(Modification)
In the third embodiment, a determination unit for determining whether the input voltage of the control power supply 102 has reached a predetermined voltage is provided, and the output of the control power supply 102 is controlled according to the determination result of the determination unit. Although the configuration has been described, the same effect can be obtained even if the configuration is such that the output of the oscillation unit 103 or the output of the amplification unit 104 is controlled according to the determination result of the determination unit.
[0091]
<Other embodiments>
Although the system of the present invention supplies power to the commercial power system, it is needless to say that power may be supplied to an AC power system other than the commercial AC power system, such as a private AC power generation facility in a factory or the like.
[0092]
In addition, even if the present invention is applied to a system including a plurality of devices (for example, a solar cell module, a DC / DC converter, an inverter, and the like), a device including one device (for example, a DC / DC converter) May be applied.
[0093]
Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and a computer (or CPU or MPU) of the system or apparatus to store the storage medium. It is needless to say that the present invention is also achieved by reading and executing the program code stored in the.
[0094]
In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
[0095]
As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, and the like can be used.
[0096]
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. It goes without saying that a part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0097]
Further, after the program code read from the storage medium is written into a memory provided on a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that a CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0098]
【The invention's effect】
As described above, according to the present invention, when the voltage generated from the solar cell is lower than the voltage required for the voltage of the drive signal to be equal to or higher than the predetermined threshold, the drive signal is not output. Thus, the switching element can be driven in an appropriate state, for example, in a state where the ON resistance is always small.
[0099]
Therefore, it is possible to improve the startup characteristics of the power converter in a configuration in which the voltage input to the power converter is low, such as a single cell converter in which a power converter is provided for each single cell or a small number of cells connected in series. it can.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a photovoltaic power generation system including a DC / DC converter as a power converter according to the present invention.
FIG. 2 is a block diagram showing a configuration of a conventional DC / DC converter.
FIG. 3 is a block diagram illustrating a configuration of a DC / DC converter according to a first embodiment of the present invention.
FIG. 4 is a block diagram showing a configuration of a DC / DC converter according to a second embodiment of the present invention.
FIG. 5 is a block diagram showing a configuration of a third embodiment of the DC / DC converter according to the present invention.
FIG. 6 is a graph showing a relationship between a gate voltage of a FET and an ON resistance.
FIG. 7 is a graph showing the relationship between the amount of solar radiation and the output power of a conventional DC / DC converter.
FIG. 8 is a graph showing the relationship between the amount of solar radiation and the output power of the DC / DC converter according to the first embodiment.
FIG. 9 is a diagram showing an appearance of a general household photovoltaic power generation system.
FIG. 10 is a block diagram showing a configuration of the photovoltaic power generation system of FIG.
11 is a diagram illustrating an example of a configuration of a DC / DC converter unit 72 illustrated in FIG.
[Explanation of symbols]
1 solar cell
2 DC / DC converter
3 Inverter
4 Commercial AC system
15 transformer
32 input capacitor
33, 34 switching element
36 Rectifier circuit
37 Smoothing circuit
46 Gate drive circuit
52 Inverter bridge
53 control circuit
54 input voltage detector
55 Input current detector
58 Filter
71 Grid-connected inverter
72 DC / DC converter
73 DC / AC converter
74 Control power generation unit
75 Solar cell module
76 solar cell string
101 drive circuit
102 Control power supply
103, 113 oscillator
104, 118 Amplifier
114 Reference voltage source
115 comparator
116, 117 output enable signal input terminal

Claims (1)

A power converter that boosts a DC voltage output from a solar cell,
A voltage-driven switching element,
A drive signal generation unit that generates a drive signal for the switching element;
A control power supply unit that boosts a DC voltage output from the solar cell and supplies power to the switching element and the drive signal generation unit,
A power converter comprising: a determination unit configured to perform control so as to generate the drive signal only when the voltage of the drive signal is equal to or higher than a predetermined threshold.

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