JP2004334704A - Power conversion device and control method thereof, and solar power generation device - Google Patents

Abstract

In a photovoltaic power generation system, when an inverter at an output destination of a DC / DC converter is stopped, the output of the DC / DC converter has a voltage that cannot be explained only by a voltage increase at a light load of a solar cell. As a result, the inverter needs to be designed to have an input voltage higher than necessary.
A DC / DC converter for boosting the output voltage of a solar cell includes a switching element for driving the output power of the solar cell, a driving circuit, a transformer for boosting the switched power, and a transformer for boosting the switched power. And a control circuit 147 that stops the supply of the drive pulse when the rectified voltage exceeds the upper limit voltage, and then restarts the supply of the drive pulse when the rectified voltage falls below the lower limit voltage. I do.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power conversion device, a control method thereof, and a solar power generation device.
[0002]
[Prior art]
In recent years, problems such as global warming due to emission of carbon dioxide and the like due to the use of fossil fuels, accidents at nuclear power plants 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, DC power generated by the solar cell is converted (orthogonal-converted) into AC power by an inverter or the like, and a load on a customer or a commercial power system (hereinafter, referred to as a “system”). ).
[0004]
FIG. 1 is a schematic view of a photovoltaic power generation system, and FIG. 2 is a block diagram showing connection of the photovoltaic power generation system.
[0005]
The solar cell module 75 shown in FIGS. 1 and 2 has a plurality of solar cells having an output voltage of several volts connected in series, and outputs a voltage of about 20 volts. Further, 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 an inverter for connecting one or more solar cell strings 76 to the system 72 if necessary. By connecting to 71, a grid-connected solar power generation system is constructed.
[0006]
By the way, the photovoltaic cell constituting the photovoltaic power generation system has a characteristic that the voltage changes depending on the load due to its characteristics. The open-circuit voltage under no load is always higher than the optimum operating point voltage at which the output of the solar cell is maximized. In order to use the photovoltaic cell efficiently as a power generation device, the solar cell may be operated at the optimal operating point (that is, an optimal load may be applied), but when the load becomes light (that is, the load resistance increases). As a result, the voltage of the solar cell increases. Therefore, when the inverter 71 is stopped, the voltage of the photovoltaic cells rises to the open-circuit voltage. Therefore, the power conversion device such as the inverter 71 connected to the photovoltaic string 76 in which the photovoltaic cells are connected in series causes the voltage to rise. Must be endurable.
[0007]
As a countermeasure against an increase in output voltage such as the open-circuit voltage of a solar cell, there is known a method of suppressing a voltage increase by attaching a voltage suppressing element to a solar cell or a module as shown in JP-A-2000-228529. . 3 and 4 are diagrams showing a voltage rise suppression method disclosed in JP-A-2000-228529. The bypass diode 78 and the voltage suppressing element 79 are connected in parallel to the solar cell 77, and the output voltage of the solar cell 7 is suppressed from increasing by the forward drop voltage or the Zener voltage of the voltage suppressing element 79.
[0008]
For such a photovoltaic power generation system, the present inventors have proposed a solar power generation system using a high step-up open-loop DC / DC converter (hereinafter simply referred to as “DC / DC converter”) as an effective form of the photovoltaic power generation system. A photovoltaic power generation system was studied. This photovoltaic power generation system does not have a configuration in which a large number of photovoltaic cells are serialized as in a photovoltaic module 75 or a photovoltaic string 76, and is connected to the inverter 71, but a single cell or several cells are serialized. An open-loop DC / DC converter that does not perform negative feedback control such as constant voltage control or maximum operating point tracking is arranged in the vicinity thereof to constitute a solar cell module with a DC / DC converter. Supply. The advantages of such a solar power generation system include the following.
[0009]
(1) A general solar cell module has a considerably lower output voltage than a system voltage. Therefore, when a system interconnection type photovoltaic power generation system is formed using a general solar cell module, a required voltage can only be obtained by connecting a large number of solar cell modules in series. As a result, a small-scale solar power generation system cannot be constructed. However, according to the solar cell module with a DC / DC converter, a solar cell module having a high output voltage can be configured, so that a small-capacity solar power generation system can be easily configured.
[0010]
(2) When a general solar cell module is connected in series to increase the voltage, a portion of the solar cell element in the solar cell module necessarily has a high voltage. Under such circumstances, the cost of the covering material (insulating material) of a general solar cell module increases in order to cope with a breakage of the covering. However, the solar cell module with a DC / DC converter can make the coating (insulation) of the solar cell element thinner, and as a result, it is possible to greatly reduce the cost.
[0011]
(3) When a single cell is used, a serialization step is not required, and there is no need to keep a distance between cells in series, so that the active area is wide.
[0012]
In the process of studying a photovoltaic power generation system using a solar cell module with a DC / DC converter, when the inverter at the output destination of the DC / DC converter is stopped, the inventors add the aforementioned output to the DC / DC converter. Abnormal voltage rise that cannot be explained by the voltage rise of the photovoltaic cells at light load alone has occurred, and a problem has arisen that the inverter must be designed to have a higher input voltage than necessary.
[0013]
This phenomenon will be described in more detail. For example, let the open voltage of the solar cell be Voc, the optimum operating point voltage be Vpm, and the boost ratio of an open-loop DC / DC converter operating at full duty be N. In this case, the output voltage of the DC / DC converter should be approximately Vpm × N [V] while the inverter is operating, and theoretically Voc × N [V] if the inverter stops. However, actually, when the output voltage when the inverter is stopped is measured, the output voltage is much higher than Voc × N [V]. The inventors have named this phenomenon "abnormal voltage rise".
[0014]
[Patent Document]
JP 2000-228529 A
[0015]
[Problems to be solved by the invention]
The present invention is to solve the above-mentioned problems individually or collectively, and aims at suppressing an abnormal voltage rise.
[0016]
[Means for Solving the Problems]
The present invention has the following configuration as one means for achieving the above object.
[0017]
According to the present invention, a power conversion device that boosts an output voltage of a solar cell includes a driving circuit that supplies a driving pulse to a switching circuit that switches output power of the solar cell, a transformer that boosts the switched power, It is characterized by having a rectifier circuit for rectifying power and a voltage suppression circuit for suppressing the voltage of the rectified power.
[0018]
Further, the control method of the present invention is the control method of the power conversion device, wherein the supply of the drive pulse is stopped when the rectified voltage exceeds the first predetermined value, and thereafter, the rectified voltage is reduced from the first predetermined value. It is characterized in that the supply of the drive pulse is restarted when the value falls below the second predetermined low value, or the drive pulse is thinned out when the rectified voltage exceeds the predetermined value.
[0019]
Further, a solar power generation device according to the present invention includes a solar cell, the above-described power conversion device, and an inverter that converts DC power output from the power conversion device into AC power.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a photovoltaic power generation system (apparatus) according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0021]
The inventors have developed a “high step-up open-loop DC / DC converter” as one effective form of a photovoltaic power generation system. As a result, when the inverter connected as a load of the DC / DC converter does not input a sufficient current or when the inverter is stopped, an abnormal voltage rise occurs, and the inverter is required to have an unnecessarily high withstand voltage. Encountered. Hereinafter, the system using the DC / DC converter, the configuration and operation of the DC / DC converter, and the abnormal voltage rise and its countermeasures will be described step by step.
[0022]
[First embodiment]
[Configuration of solar power generation system]
FIG. 5 is a block diagram illustrating a configuration example of a photovoltaic power generation system using a DC / DC converter.
[0023]
The power generated by the solar cell 1 is boosted by the DC / DC converter 2, converted into AC power by the inverter 3, and connected to the grid 4. In the system shown in FIG. 5, a plurality of sets of a solar cell 1 and a DC / DC converter 2 are connected in parallel and connected to an inverter 3 to constitute a system interconnection system in which reverse power flows from the inverter 3 to the system 4. I do.
[0024]
● Solar cells
The solar cell 1 is installed outdoors such as a roof where sunlight is not blocked, and is configured so that the number of series connections is limited and the output voltage is low. As the solar cell 1, an amorphous silicon-based, polycrystalline silicon-based, crystalline silicon-based solar cell, or the like can be used. In the embodiment, a stacked solar cell in which three layers of amorphous silicon are stacked is used for the solar cell 1. The characteristics are shown below. FIG. 6 is a diagram showing output characteristics of the solar cell 1.
Rated solar radiation 1 kW / m ² Ambient temperature 25 ° C
Short-circuit current Isc = 12.45 A
Open voltage Voc = 1.4V
Maximum operating point current Ipm = 10.0A
Maximum operating point voltage Vpm = 1.0V
Maximum output power Pmax = 10W
[0025]
● DC / DC converter
An open loop converter 2 is provided near the 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 is for reducing the power transmission loss in the power transmission path up to the inverter 3 arranged indoors, for example. It should be noted that the solar cell 1 and the DC / DC converter 2 may be configured as an integrated (laminated) module. By doing so, the wiring between the solar cell 1 and the DC / DC converter 2 can be shortened, and loss due to wiring resistance can be effectively reduced.
[0026]
The gate drive circuit 46 of the DC / DC converter 2 supplies two gate drive signals having opposite phases to the gates of the switching elements 33 and 34 constituting the push-pull switching circuit. Although the duty is fixed because of the gate drive signal (rectangular wave), the maximum duty of the push-pull switching circuit is preferably 50% because of its high conversion efficiency. The reason why the duty of the gate drive signal is fixed is to reduce the cost and improve the reliability by simplifying the switching control circuit by eliminating the feedback circuit. The switching frequency is set between 20 kHz and several hundred kHz due to a trade-off between power loss due to switching and miniaturization of the transformer.
[0027]
Since the output voltage of the solar cell 1 is low, the switching elements 33 and 34 are preferably MOSFETs with low on-resistance. At present, MOSFETs, which are unipolar elements, are particularly excellent in terms of on-resistance.
[0028]
As the input capacitor 32, it is preferable to use a capacitor having a small equivalent series resistance (ESR) and an excellent high-frequency characteristic so that the power supply source of the DC / DC converter 2 can be regarded as a voltage source. ), A multilayer ceramic capacitor, a tantalum electrolytic capacitor or the like having a small ESR can be used. With the input capacitor 32, the power supply source of the DC / DC converter 2 can be regarded as a voltage source, and the DC / DC converter 2 becomes what is called a voltage type converter.
[0029]
The transformation ratio (turn ratio) of the transformer 15 is such that 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 when the operating voltage of the solar cell 1 is minimum. 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.
[0030]
The optimal operating point of a solar cell has the characteristic that the voltage becomes low at high temperature and low solar radiation. In the embodiment, the minimum operation voltage of the solar cell is set to 0.75 V, and at that time, the winding ratio that allows the output voltage to be raised to 150 V is set in the transformer 15.
Turn ratio 0.75: 150
Primary winding 2 turns x 2
Secondary winding 400 turns
[0031]
A rectifier circuit 36 for rectifying the high-frequency AC output of the transformer 15 and a smoothing circuit 37 for smoothing are provided at the subsequent stage of the transformer 15. If the capacitance of the input capacitor 51 of the inverter 3 which is the output destination of the DC / DC converter 2 is sufficiently large, the capacitor of the smoothing circuit 37 may not be provided.
[0032]
DC power is input from the solar cell 1 to the DC / DC converter 2. 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 then supplied to the inverter 3.
[0033]
Since the conversion efficiency of the DC / DC converter 2 is approximately 95%, the maximum output power of the DC / DC converter 2 is about 95% of the maximum output power of the solar cell 1.
[0034]
● Inverter
The control circuit 53 of the inverter 3 monitors the voltage and 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 performs the maximum power tracking control (MPPT control) of the DC / DC converter 2 and the solar cell 1 together, so that the power generated by the solar cell 1 is effectively used.
[0035]
The inverter 3 of the present embodiment is operated in an input voltage range of 150 V to 250 V by MPPT control. This input voltage range is determined by a change in the maximum power point due to solar radiation and temperature of the solar cell 1, a transformation ratio of the DC / DC converter 2, and a switching duty. In the DC / DC converter 2 of the present embodiment, the on-duty of the boost switching is fixed, so that the on-duty does not affect the boost ratio.
[0036]
The DC power input to the inverter 3 is converted into AC power by the filter 58 including the inverter bridge 52 and the interconnection reactor, and is supplied to the grid 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, a number of well-known and publicly-known methods are known, and the description thereof is omitted.
[0037]
By such PWM control of the inverter 3, while extracting the maximum power from the solar cell 1 and the DC / DC converter 2 (MPPT control), AC power having the same current phase as the system 4 and having a power factor of 1 is output.
[0038]
[Operation of DC / DC converter]
An output characteristic of the DC / DC converter 2 in the above configuration in a state where an output voltage suppressing circuit described later is not provided will be described.
[0039]
When the inverter 3 which is the output destination of the DC / DC converter 2 is stopped, the converter 2 and the solar cell 1 are almost in no load (the output current is almost zero). That is, the solar cell 1 operates at the point A shown in FIG. 6, and the converter 2 receives a voltage 1.4 times the rated voltage.
[0040]
Since the duty of the switching circuit of the DC / DC converter 2 is fixed, the ratio between the input voltage and the output voltage becomes constant during normal load operation. Accordingly, the output voltage of the DC / DC converter 2 is represented by the following equation, and the operating point voltage of the solar cell 1 and the output voltage of the DC / DC converter 2 fluctuate in proportion.
Vd = Tr × Vop
Here, Vd is the output voltage of the DC / DC converter 2
Vop is the operating voltage of the solar cell 1
Tr is the boost ratio (turn ratio)
[0041]
However, when there is no load or when the load current is small, an abnormal voltage rise occurs. As a result, rated solar radiation 1 kW / m ² The IV curve characteristic of the DC / DC converter 2 at the time of irradiation is as shown in FIG. 7, and the no-load voltage becomes 450 V (point B) even though the output voltage at the time of maximum power output is 200 V. In FIG. 7, the voltage at the time of low current becomes a high voltage (from 280 to 450 V) is caused by an abnormal voltage rise.
[0042]
[Voltage suppression circuit]
FIG. 8 is a block diagram illustrating a configuration example in which an output voltage suppression circuit is attached to the DC / DC converter 2.
[0043]
When the inverter 3 is operating normally, the output voltage suppression circuit does not operate. This is because the output voltage of the DC / DC converter 2 is controlled in the range of 150 V to 250 V by the MPPT control of the inverter 3. That is, the output voltage suppression circuit prevents the abnormal voltage rise shown in FIG. 7 from occurring when the inverter 3 is stopped or enters a low current output state due to some abnormality, in other words, the output voltage of the DC / DC converter 2 The DC / DC converter 2 is controlled so as not to exceed the voltage (upper limit voltage). Further, the DC / DC converter 2 is controlled so that the output voltage of the DC / DC converter 2 does not become lower than a predetermined voltage (lower limit voltage) so that the system interconnection operation can be performed immediately after the operation of the inverter 3 is restarted. I do.
[0044]
● Output voltage detection circuit
The output voltage detection circuit 63 is a resistor voltage divider provided between the smoothing circuit 37 and the output terminal of the DC / DC converter 2 to detect the output voltage of the DC / DC converter 2. The output voltage detection circuit 63 divides the output voltage of the DC / DC converter 2 into a low voltage that is easy for signal processing, and sends it to the comparators 84 and 85.
[0045]
● Reference voltage source
The reference voltage sources Vref1 and Vref2 supply voltages to be compared with the voltage supplied from the output voltage detection circuit 63 (voltages corresponding to the above upper limit voltage and lower limit voltage).
[0046]
In this embodiment, the upper limit voltage is set to 300 V for the following reason. In the IV curve characteristics shown in FIG. 7, when the voltage rise due to the solar cell 1 and the abnormal voltage rise due to the DC / DC converter 2 are separated, a voltage V1 or less represented by the following equation is a voltage rise due to the solar cell 1 and a voltage exceeding V1. Can be determined as an abnormal voltage rise due to the DC / DC converter 22.
V1 = Voc × Ns / Np
Here, Voc is an open circuit voltage
Np is the number of primary windings of the transformer 15
Ns is the number of secondary windings of the transformer 15
[0047]
Since the open-circuit voltage Voc of the solar cell 1 is 1.4 V, the number of primary windings Np of the transformer 15 is Np = 2, and the number of secondary windings Ns is 400, V1 = 280 V. The upper limit voltage is set to 300 V which is slightly higher than 280 V in consideration of the error of the resistor.
[0048]
On the other hand, the lower limit voltage is set to 250 V or more, which is the upper limit of the MPPT operation range, which is the normal operation range of the inverter 3, in consideration of restarting the system interconnection operation immediately after the inverter 3 returns to the normal operation. . When a backflow prevention diode is inserted in series with the output of the DC / DC converter 2 or the input of the inverter 3, it is necessary to add the forward voltage drop to the lower limit voltage. For example, if the forward voltage drop of the backflow prevention diode is 1 V, the lower limit voltage is set to 251 V or more. Of course, it is necessary to consider the voltage drop due to the resistance of the wiring between the DC / DC converter 2 and the inverter 3. In consideration of the above, the lower limit voltage of this embodiment is set to 255V.
[0049]
● Control circuit
Control circuit 147 receives output signals SIG1 and SIG2 of comparators 84 and 85, and outputs signal SIG3 to AND circuit 146. When it is necessary to insulate the primary and the secondary of the transformer 15, a photocoupler or the like is provided at the output of the control circuit 147 to provide an insulation function.
[0050]
● AND circuit
AND circuit 146 receives a gate drive pulse of 50% duty from gate drive circuit 46, receives signal SIG3 from control circuit 147, and outputs a logical product signal of these signals to gate pulse signals G1 and G1 of switching elements 33 and 34. Output as G2.
[0051]
● Operation of DC / DC converter
FIGS. 9 and 10 are diagrams illustrating the operation of the DC / DC converter 2 having the above-described output voltage suppression circuit. The DC / DC converter 2 when the inverter 3 stops at the timing t1 and resumes operation at the timing t4. Will be described.
[0052]
When the inverter 3 performs the MPPT operation before the timing t1, the output voltage of the DC / DC converter 2 is in the inverter MPPT operation voltage range shown in FIG. When the inverter 3 stops at the timing t1, the output voltage of the DC / DC converter 2 decreases in the direction of the arrow A shown in FIG. After charging, the output voltage gradually increases (period from t1 to t3 shown in FIG. 9), and at timing t2, the output voltage of the DC / DC converter 2 reaches the lower limit voltage (255 V), and the output signal SIG2 of the comparator 85 Changes from the L level to the H level.
[0053]
When the output voltage of the DC / DC converter 2 reaches the upper limit voltage (300 V) at timing t3, the output signal SIG1 of the comparator 84 changes from L level to H level, and the output signal SIG3 of the control circuit 147 changes from H level to L level. Transition to the level (see FIG. 11). When signal SIG3 is at the L level, AND circuit 146 stops outputting drive pulses G1 and G2 (see FIG. 12), and the output voltage of DC / DC converter 2 is smoothed by the capacitor of smoothing circuit 37 and the input of inverter 3 With the discharge of the capacitor, it gradually decreases (period from t3 to t4 shown in FIG. 9). When the output voltage of DC / DC converter 2 falls below the upper limit voltage (300 V), signal SIG1 transitions from H level to L level, but the state of signal SIG3 does not transition and remains at L level (FIG. 11). reference).
[0054]
When the output voltage of the DC / DC converter 2 reaches the lower limit voltage (255 V) at the timing t4, the signal SIG2 changes from the H level to the L level, and the signal SIG3 changes from the L level to the H level (see FIG. 11). The AND circuit 146 restarts the output of the drive pulses G1 and G2. It should be noted that although SIG1 does not normally go high and SIG2 does not go low due to the relationship between Vref1 and Vref2, FIG. 11 shows all the states of SIG1, SIG2 and SIG3.
[0055]
Thereafter, while the inverter 3 is stopped, the DC / DC converter 2 repeats the same operation from t2 to t4. When the inverter 3 resumes operation at the timing t6, the output voltage of the DC / DC converter 2 becomes the inverter MPPT operating voltage. After moving to the range (in the direction of arrow B shown in FIG. 10) and reaching the lower limit voltage (255 V) (t7), the signal SIG2 goes low and the signal SIG3 goes high, and the AND circuit 146 sets the drive pulse G1 G2 is output. After that, the output voltage of the DC / DC converter 2 is maintained in the inverter MPPT operating voltage range, so that the AND circuit 146 maintains the output of the drive pulse.
[0056]
As described above, while the operation of the inverter 3 is stopped due to a power failure or the like, the DC / DC converter 2 maintains the output voltage in the range from the lower limit voltage to the upper limit voltage while preventing an abnormal voltage rise. Further, when the inverter 3 returns to the normal operation, the DC / DC converter 2 automatically shifts to the normal operation. As a result, when a power failure or the like is restored, the inverter 3 can quickly restart the system interconnection operation.
[0057]
[Second embodiment]
Hereinafter, a solar power generation system according to a second embodiment of the present invention will be described. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0058]
In the second embodiment, an example will be described in which when the output voltage of the DC / DC converter 2 reaches the upper limit voltage, the drive pulse is not completely stopped and the drive pulse is thinned out.
[0059]
FIG. 13 is a block diagram illustrating a configuration example of the DC / DC converter 2 according to the second embodiment. Unlike the DC / DC converter 2 of the first embodiment, the reference voltage is one corresponding to the “suppression voltage”.
[0060]
If the suppression voltage is set to 250 V or more, which is the upper limit of the operation range of the inverter MPPT, the DC / DC converter 2 is set to the output voltage suppression operation when the inverter 3 stops, and the DC / DC converter 2 is set to the normal operation when the inverter 3 resumes operation. It is possible to drive. However, when a backflow prevention diode is inserted in series with the output of the DC / DC converter 2 or the input of the inverter 3, the forward voltage drop or the voltage drop of the wiring is added to the suppression voltage as described above. Therefore, the suppression voltage is set to 255 V in consideration of these factors.
[0061]
FIGS. 14 and 15 are diagrams for explaining the operation of the DC / DC converter 2 having the above-described output voltage suppression circuit. The DC / DC converter 2 when the inverter 3 stops at the timing t1 and resumes operation at the timing t3. Will be described.
[0062]
If the inverter 3 is performing the MPPT operation before the timing t1, the output voltage of the DC / DC converter 2 is from 150 V to 250 V in the inverter MPPT operation voltage range shown in FIG. When the inverter 3 stops at the timing t1, the output voltage of the DC / DC converter 2 decreases and the output voltage moves in the direction of arrow A shown in FIG. After charging, the output voltage gradually increases (period from t1 to t3 shown in FIG. 14). At timing t2, the output voltage of the DC / DC converter 2 reaches the suppression voltage (255 V), and the output signal SIG4 of the comparator 184. Changes from the L level to the H level.
[0063]
When the signal SIG4 becomes H level, the control circuit 148 causes the output signal SIG5 to transition from the H level to a thinning pattern (see FIG. 14) (thinning mode). The AND circuit 146 outputs a logical product signal of the drive pulse supplied from the gate drive circuit 46 and the pulse of the thinning pattern as drive pulses G1 and G2. Therefore, the number of drive pulses is reduced, and the output voltage of the DC / DC converter 2 is suppressed.
[0064]
Note that a gate drive circuit 46 supplies a synchronization signal SYNC (or a drive pulse or a clock signal) to the control circuit 148 in order to synchronize the pulse of the thinning pattern with the drive pulse. Further, in order to prevent the transformer 15 from being demagnetized, the width of each pulse of the thinning pattern is adjusted to the sum of the pulse widths of the drive pulses G1 and G2 supplied from the gate drive circuit 46. Furthermore, the thinning rate of the drive pulse may be set so that the output voltage of the DC / DC converter 2 is suppressed to a target maximum voltage (for example, 300 V).
[0065]
Thus, while the inverter 3 is stopped, the output voltage of the DC / DC converter 2 is suppressed by the thinning pattern.
[0066]
Next, when the inverter 3 resumes operation at the timing t3, the output voltage of the DC / DC converter 2 moves to the inverter MPPT operating voltage range (the direction of the arrow B shown in FIG. 15) and reaches the suppression voltage (255 V). Then, (t4), the signal SIG4 becomes L level and the signal SIG5 becomes H level (decimation mode is released), and the AND circuit 146 outputs drive pulses G1 and G2 without thinning. After that, the output voltage of the DC / DC converter 2 is maintained in the inverter MPPT operating voltage range, so that the AND circuit 146 maintains the output of the normal drive pulse.
[0067]
Thus, while the operation of the inverter 3 is stopped due to a power failure or the like, the DC / DC converter 2 maintains the output voltage at the target maximum voltage while preventing an abnormal voltage rise. Further, when the inverter 3 returns to the normal operation, the DC / DC converter 2 automatically shifts to the normal operation. As a result, when a power failure or the like is restored, the inverter 3 can quickly restart the system interconnection operation.
[0068]
[Third embodiment]
Hereinafter, a solar power generation system according to a second embodiment of the present invention will be described. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0069]
In the above-described first and second embodiments, the case where the inverter 3 has the MPPT control function, but uses an inverter of constant input voltage control will be described as a third embodiment. In this case, the configuration of the DC / DC converter 2 is the same as that of FIGS. 8 and 13, but the setting of the lower limit voltage in the first embodiment and the setting of the suppression voltage in the second embodiment are different.
[0070]
● Setting of lower limit voltage
When connecting an inverter of constant input voltage control, the lower limit voltage may be set to a value equal to or higher than a voltage value at which the inverter normally operates. For example, if the lower limit of the normal operating voltage of the inverter is 200 V, the lower limit voltage is set to 200 V or more. Of course, the forward voltage drop of the backflow prevention diode and the voltage drop of the wiring are also taken into consideration.
[0071]
● Setting of suppression voltage
When an inverter of constant input voltage control is connected, the suppression voltage may be set to a value equal to or higher than the voltage at which the inverter operates normally. Of course, the forward voltage drop of the backflow prevention diode and the voltage drop of the wiring are also taken into consideration.
[0072]
As described above, if the lower limit voltage or the suppression voltage is set, the DC / DC converter 2 operates in the same manner as in the first or second embodiment, and can suppress an abnormal voltage rise.
[0073]
According to each of the above-described embodiments, the abnormal voltage rise of the open loop converter that receives the power generated by the solar cell as an input is suppressed, and the inverter that is the output (connection) destination of the DC / DC converter is set to a higher input voltage It does not need to be designed at the same time, contributing to the reduction of the total cost of the photovoltaic power generator (system) including the inverter.
[0074]
In addition, even when the inverter is stopped due to a power failure or the like, the DC / DC converter prevents an abnormal voltage rise and maintains the output voltage equal to or lower than the set voltage. As a result, the inverter is ready to be started, and when the power failure or the like is resolved and the operation of the inverter is restarted, the inverter can immediately start the system interconnection operation.
[0075]
【The invention's effect】
As described above, according to the present invention, an abnormal voltage rise can be suppressed. Accordingly, there is no need to design the inverter to which the DC / DC converter is connected to an input voltage that is higher than necessary, which contributes to a reduction in the total cost of the photovoltaic power generator (system) including the inverter.
[Brief description of the drawings]
FIG. 1 is an overview of a photovoltaic power generation system,
FIG. 2 is a block diagram showing connection of a solar power generation system;
FIG. 3 is a diagram showing a voltage rise suppression method;
FIG. 4 is a diagram showing a voltage rise suppression method;
FIG. 5 is a block diagram showing a configuration example of a photovoltaic power generation system using a DC / DC converter.
FIG. 6 is a diagram showing output characteristics of a solar cell.
FIG. 7 is a diagram showing IV curve characteristics of a DC / DC converter.
FIG. 8 is a block diagram showing a configuration example in which an output voltage suppression circuit is attached to a DC / DC converter;
FIG. 9 illustrates an operation of a DC / DC converter having an output voltage suppression circuit.
FIG. 10 illustrates an operation of a DC / DC converter having an output voltage suppression circuit.
FIG. 11 is a diagram showing an input / output relationship of a control circuit;
FIG. 12 is a diagram showing an input / output relationship of an AND circuit;
FIG. 13 is a block diagram illustrating a configuration example of a DC / DC converter 2 according to the second embodiment;
FIG. 14 illustrates an operation of a DC / DC converter having an output voltage suppression circuit.
FIG. 15 is a diagram illustrating the operation of a DC / DC converter having an output voltage suppression circuit.

Claims (13)

A power converter for boosting an output voltage of a solar cell,
A drive circuit that supplies a drive pulse to a switching circuit that switches output power of the solar cell,
A transformer that boosts the switched power,
A rectifier circuit for rectifying the boosted power;
A power conversion device comprising: a voltage suppression circuit that suppresses a voltage of rectified power. The power converter according to claim 1, wherein the power converter is an open loop. The voltage suppression circuit stops supplying the drive pulse when the rectified voltage exceeds a first predetermined value, and thereafter, when the rectified voltage falls below a second predetermined value lower than the first predetermined value. The power converter according to claim 1 or 2, wherein the supply of the driving pulse is restarted. 4. The power converter according to claim 3, wherein the first predetermined value is Voc × n, where Voc is an open-circuit voltage of the solar cell and n is a transformation ratio of the transformer. 5. The said 2nd predetermined value is more than the upper limit of the MPPT input voltage range of the inverter which has an MPPT function and is connected as the load of the said power converter, The Claim 3 or Claim 4 characterized by the above-mentioned. Power converter. The said 2nd predetermined value is more than the fixed control voltage value of the inverter which is connected as a load of the said electric power converter and has an input voltage constant control function, The Claim 3 or Claim 4 characterized by the above-mentioned. Power converter. The power converter according to claim 1, wherein the voltage suppression circuit thins out the drive pulse when the rectified voltage exceeds a predetermined value. The power converter according to claim 7, wherein the predetermined value is equal to or larger than an upper limit value of an MPPT input voltage range of an inverter having an MPPT function, which is connected as a load of the power converter. The power converter according to claim 7, wherein the predetermined value is equal to or higher than a constant control voltage value of an inverter connected as a load of the power converter and having an input voltage constant control function. A detector that detects an input value from the solar cell, a driving circuit that supplies a driving pulse to a switching circuit that switches output power of the solar cell, a transformer that boosts the switched power, and rectifies the boosted power. A control method of a power conversion device having a rectifier circuit and boosting an output voltage of the solar cell,
When the rectified voltage exceeds a first predetermined value, the supply of the drive pulse is stopped, and thereafter, when the rectified voltage falls below a second predetermined value lower than the first predetermined value, the supply of the drive pulse is restarted. A control method characterized in that: A detector that detects an input value from the solar cell, a driving circuit that supplies a driving pulse to a switching circuit that switches output power of the solar cell, a transformer that boosts the switched power, and rectifies the boosted power. A control method of a power conversion device having a rectifier circuit and boosting an output voltage of the solar cell,
When the rectified voltage exceeds a predetermined value, the drive pulse is thinned out. Solar cells,
A power converter according to any one of claims 1 to 9,
An inverter for converting DC power output from the power converter to AC power. Multiple solar cells,
The plurality of power converters according to any one of claims 1 to 9, which are connected to the plurality of solar cells, respectively.
An inverter for converting DC power output from the plurality of power converters into AC power.

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