JP2014036491A - Dc/dc power conversion device, and power conditioner for photovoltaic system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC/DC power conversion device and a power conditioner for a photovoltaic system which inexpensively and highly efficiently implement a lower withstanding voltage of each component constituting a DC voltage conversion section.SOLUTION: A DC/DC power conversion device comprises: a DC voltage conversion section 3 having switching elements 5 and 6, a charge/discharge capacitor 9 to be charged/discharged as those elements are turned on/off, and diodes 7 and 8 for providing charging/discharging paths; voltage dividing capacitors 10 and 11 connected in series with each other; a first voltage equalizing diode 12 connected forward in a direction to allow a current flow from a negative terminal of the charge/discharge capacitor 9 to the junction of the voltage dividing capacitors 10 and 11; a first voltage equalizing Zener diode 13 connected in an anti-series relationship thereto; a second voltage equalizing diode 15 connected forward in a direction to allow a current flow from the junction of the voltage dividing capacitors 10 and 11 to a positive terminal of the charge/discharge capacitor 9; and a second voltage equalizing Zener diode 16 connected in an anti-series relationship thereto.

Description

  The present invention relates to a DC / DC power converter and a power conditioner for a photovoltaic power generation system including the DC / DC power converter.

  A conventional DC / DC power converter performs on / off voltage operation from a direct current to a direct current by controlling the amount of energy stored in and discharged from a reactor by using an on / off operation of a semiconductor switch. Since this reactor has a large and heavy problem, the voltage applied to the reactor is reduced using charging and discharging of the capacitor, and the inductance value required for the reactor is reduced to make the reactor smaller and lighter. A technique for realizing this is disclosed (for example, Patent Document 1).

  In the above prior art, during normal operation (hereinafter referred to as “steady state”), the voltage across the charge / discharge capacitor can be controlled to an arbitrary value, so that the voltage applied to the switching elements and diodes constituting the DC voltage conversion unit Therefore, the withstand voltage of the switching element, the diode element, and the charge / discharge capacitor can be made lower than the voltage of the smoothing capacitor, and there are advantages such as a reduction in component costs and an improvement in power generation efficiency.

JP-A-61-92162

  However, in the above prior art, for example, the DC / DC power converter stops normal operation, and the switching elements constituting the DC voltage converter are not on / off controlled (hereinafter referred to as “control stop state”). When the voltage of the DC power supply suddenly drops to zero or near zero while the voltage remains in the charge / discharge capacitor and the smoothing capacitor, the smoothing capacitor and the charge / discharge capacitor have their own internal ESR (equivalent Series resistance: Equivalent Series Resistance), and a situation where discharge is caused by a leakage current of a switching element and a diode constituting a DC voltage converter may occur. In general, since the capacity of the charge / discharge capacitor is smaller than the capacity of the smoothing capacitor, the charge / discharge capacitor discharges faster than the smoothing capacitor discharges. At this time, when the voltage between the terminals of the charge / discharge capacitor suddenly decreases to almost zero, the smoothing capacitor and the diode connected in series with the charge / discharge capacitor are connected in parallel, and the voltage of the smoothing capacitor at this time, That is, a voltage near the output voltage in the steady state of the DC / DC power converter may be transiently applied to this diode. For this reason, it is necessary to make the element withstand voltage of the diode connected in series with the charge / discharge capacitor larger than the maximum output voltage of the DC / DC power converter, which causes an extra cost increase and a decrease in efficiency.

  The present invention has been made in view of the above, and can reduce the withstand voltage of each component constituting the direct-current voltage conversion unit, and can achieve a low-cost and high-efficiency DC / DC power conversion device and sunlight. An object is to provide a power conditioner for a power generation system.

  In order to solve the above-described problems and achieve the object, a DC / DC power converter according to the present invention includes a reactor connected to a DC power source, a plurality of switching elements connected to the reactor, and an on-state of the switching elements. A DC voltage converter having a charge / discharge capacitor that is charged / discharged by turning off / off, and a plurality of diodes that provide a charge path and a discharge path of the charge / discharge capacitor, and is connected to the DC voltage converter and connected in series to each other An output-side smoothing capacitor having a plurality of voltage-dividing capacitors, and a first voltage equalization that is forward-connected in a direction in which a current flows from a negative-side terminal of the charge / discharge capacitor to a connection point of the voltage-dividing capacitors. A first voltage equalizing Zener diode connected in reverse series with the first voltage equalizing diode; A second voltage equalizing diode that is forward-connected in a direction in which a current flows from the mutual connection point of the voltage dividing capacitor to the positive terminal of the charge / discharge capacitor, and in anti-series with the second voltage equalizing diode. And a second voltage equalizing Zener diode connected thereto.

  ADVANTAGE OF THE INVENTION According to this invention, the proof pressure of each component which comprises a direct-current voltage conversion part can be made smaller, and low-cost and highly efficient DC / DC power converter device and the power conditioner for solar power generation systems are obtained. There is an effect that can be.

FIG. 1 is a diagram illustrating a configuration example of a DC / DC power converter according to an embodiment. FIG. 2 is a diagram illustrating each operation mode in a steady state of the DC / DC power conversion apparatus according to the embodiment. FIG. 3 is a diagram illustrating the operation mode transition when the step-up ratio is less than twice in the steady state of the DC voltage conversion unit according to the embodiment. FIG. 4 is a diagram illustrating operation mode transition when the step-up ratio is twice or more in the steady state of the DC voltage conversion unit according to the embodiment. FIG. 5 is a diagram illustrating a current path when an input voltage is applied in a control stop state of the DC / DC power converter according to the embodiment. FIG. 6 is a diagram illustrating a current path when the input voltage suddenly decreases in the control stop state of the DC / DC power converter according to the embodiment. FIG. 7 is a diagram showing the transition of each part voltage when the input voltage suddenly decreases in the control stop state of the conventional DC / DC power converter. FIG. 8 is a diagram illustrating the transition of each part voltage when the input voltage suddenly decreases in the control stop state of the DC / DC power converter according to the embodiment. FIG. 9 is a diagram illustrating an example in which the DC / DC power converter according to the embodiment is connected to a load. FIG. 10 is a diagram illustrating an example in which the DC / DC power converter according to the embodiment is connected to a single-phase or three-phase power system.

  A DC / DC power converter and a power conditioner for a photovoltaic power generation system according to embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

Embodiment.
FIG. 1 is a diagram illustrating a configuration example of a DC / DC power converter according to an embodiment. As shown in FIG. 1, the DC / DC power converter according to the embodiment boosts the input voltage Vin input from the DC power source 1 to a voltage equal to or higher than Vin by the DC voltage converter 3, and outputs the boosted voltage. The voltage Vout is output by being smoothed by the smoothing capacitor 4.

  The DC / DC power converter according to the embodiment includes an energy storage reactor 2, a DC voltage converter 3 that boosts an input voltage Vin to an output voltage Vout, and a voltage that is boosted by the DC voltage converter 3 The DC voltage converter 3 includes two switching elements 5 and 6, two diodes 7 and 8, and a charge / discharge capacitor 9. Each of the switching elements 5 and 6 is formed of a MOSFET, for example, and is turned on when the gate signal is High.

  The output-side smoothing capacitor 4 is configured by connecting two voltage dividing capacitors 10 and Co11 in series. Further, as a feature of the first embodiment, the first voltage equalizing diode 12, the first A voltage equalizing Zener diode 13, a first current limiting resistor 14, a second voltage equalizing diode 15, a second voltage equalizing Zener diode 16, and a second current limiting resistor 17 are provided.

  The DC power supply 1 has a high-voltage side terminal connected to the input terminal VL and a low-voltage side terminal connected to the reference voltage terminal Vcom. Of the two voltage dividing capacitors 10 and 11 constituting the smoothing capacitor 4 on the output side, the low voltage side terminal of one voltage dividing capacitor 10 is the reference voltage terminal Vcom, and the high voltage side terminal of the other voltage dividing capacitor 11 is It is connected to the output terminal VH. Also, the two switching elements 5 and 6 and the two diodes 7 and 8 constituting the DC voltage conversion unit 3 are sequentially connected in series, the source terminal of the switching element 5 is the reference voltage terminal Vcom, and the cathode terminal of the diode 8 is the output. A connection point between the terminal VH and the drain terminal of the switching element 6 and the anode terminal of the diode 7 is connected to the input terminal VL via the reactor 2. The charge / discharge capacitor 9 has a low-voltage side terminal at the connection point between the drain terminal of the switching element 5 and the source terminal of the switching element 6, and a high-voltage side terminal between the cathode terminal of the diode 7 and the anode terminal of the diode 8. Connected to each connection point.

  The first voltage equalizing diode 12 is forward-connected in the direction in which current flows from the negative terminal of the charge / discharge capacitor 9 to the connection point between the voltage dividing capacitors 10 and 11, and the first voltage equalizing Zener. The diode 13 is connected in anti-series with the first voltage equalizing diode 12. In the example illustrated in FIG. 1, the first current limiting resistor 14 is provided in series with the first voltage equalizing diode 12 and the first voltage equalizing Zener diode 13. The first current limiting resistor 14 may not be provided. The effect and operation of providing the first current limiting resistor 14 will be described later.

  The second voltage equalizing diode 15 is forwardly connected in a direction in which a current flows from the connection point between the voltage dividing capacitors 10 and 11 to the positive terminal of the charge / discharge capacitor 9, and the second voltage equalizing Zener. The diode 16 is connected in anti-series with the second voltage equalizing diode 15. In the example shown in FIG. 1, a configuration in which the second current limiting resistor 17 is provided in series with the second voltage equalizing diode 15 and the second voltage equalizing Zener diode 16 is shown. The second current limiting resistor 17 may not be provided. The effect and operation of providing the second current limiting resistor 17 will be described later.

  Next, the operation in the steady state of the DC / DC power converter according to the embodiment will be described. The steady state refers to a state in which the switching elements 5 and 6 are on / off controlled and the output voltage Vout is stably obtained.

  FIG. 2 is a diagram illustrating each operation mode in a steady state of the DC / DC power conversion apparatus according to the embodiment. In the example shown in FIG. 2, the first voltage equalizing diode 12, the first voltage equalizing Zener diode 13, the first current limiting resistor 14, the second voltage equalizing diode 15, and the second voltage The equalizing Zener diode 16 and the second current limiting resistor 17 are omitted.

  As shown in FIG. 2, there are four operation modes of mode 1 to mode 4 as operation modes in a steady state of the DC / DC power converter according to the embodiment. In mode 1 shown in FIG. 2A, the switching element 5 is turned on and the switching element 6 is turned off, and energy is stored in the charge / discharge capacitor 9. In mode 2 shown in FIG. 2B, the switching element 5 is turned off and the switching element 6 is turned on, and the charge / discharge capacitor 9 is released. In mode 3 shown in FIG. 2C, both the switching elements 5 and 6 are turned off, and the energy of the reactor 2 is released. In mode 4 shown in FIG. 2D, the switching elements 5 and 6 are both turned on, and energy is stored in the reactor 2. By appropriately adjusting the time ratio of each of these operation modes, the input voltage Vin input between the VL terminal and the Vcom terminal is boosted to an arbitrary voltage and output as the output voltage Vout between the VH terminal and the Vcom terminal. be able to.

  Here, the DC / DC power converter according to the embodiment operates in a steady state when the step-up ratio N of the output voltage Vout with respect to the input voltage Vin is less than twice or more than twice. Different.

  First, the operation when the boost ratio N is less than 2 will be described. FIG. 3 is a diagram illustrating the operation mode transition when the step-up ratio is less than twice in the steady state of the DC voltage conversion unit according to the embodiment.

  In FIG. 3, when the step-up ratio N is less than twice, the gate signal voltage waveform of each of the switching elements 5 and 6, the current waveform IL of the reactor 2, the current waveform Icf of the charge / discharge capacitor 9, and the charge / discharge capacitor 9 shows an inter-terminal voltage Vcf. In a steady state, the inter-terminal voltage Vcf of the charge / discharge capacitor 9 is controlled to be about ½ of the output voltage Vout, and the input voltage Vin, output voltage Vout, and terminals of the charge / discharge capacitor 9 are controlled. The magnitude relationship of the inter-voltage Vcf is as follows.

  Vout> Vin> Vcf

  When the gate signal of the switching element 5 is high and the gate signal of the switching element 6 is low (mode 1), the switching element 5 is on and the switching element 6 is off. The energy is transferred to the charge / discharge capacitor 9.

  DC power source 1 → reactor 2 → diode 7 → charge / discharge capacitor 9 → switching element 5

  Next, in the state where the gate signal of the switching element 5 is Low and the gate signal of the switching element 6 is Low (mode 3), the switching elements 5 and 6 are both turned off, so that they are accumulated in the reactor 2 through the following path. The accumulated energy is superimposed on the DC power source 1 and transferred to the voltage dividing capacitors 10 and 11.

  DC power source 1 → reactor 2 → diode 7 → diode 8 → voltage dividing capacitor 11 → voltage dividing capacitor 10

  Next, when the gate signal of the switching element 5 is Low and the gate signal of the switching element 6 is High (mode 2), the switching element 5 is turned off and the switching element 6 is turned on. The energy accumulated in 9 is superimposed on the DC power source 1 and transferred to the voltage dividing capacitors 10 and 11, and the energy is accumulated in the reactor 2.

  DC power source 1 → reactor 2 → switching element 6 → charge / discharge capacitor 9 → diode 8 → voltage dividing capacitor 11 → voltage dividing capacitor 10

  Next, in the state where the gate signal of the switching element 5 is Low and the gate signal of the switching element 6 is Low (mode 3), the switching elements 5 and 6 are both turned off, so that they are accumulated in the reactor 2 through the following path. The accumulated energy is superimposed on the DC power source 1 and transferred to the voltage dividing capacitors 10 and 11.

  DC power source 1 → reactor 2 → diode 7 → diode 8 → voltage dividing capacitor 11 → voltage dividing capacitor 10

  By repeating the series of operations described above, the input voltage Vin input between the VL terminal and the Vcom terminal is boosted to an arbitrary voltage of 1 to 2 times and output as an output voltage Vout between the VH terminal and the Vcom terminal. To do.

  Next, the operation when the step-up ratio N is twice or more will be described. FIG. 4 is a diagram illustrating operation mode transition when the step-up ratio is twice or more in the steady state of the DC voltage conversion unit according to the embodiment.

  In FIG. 4, when the step-up ratio N is 2 times or more, the gate signal voltage waveform of each switching element 5, 6, the current waveform IL of the reactor 2, the current waveform Icf of the charge / discharge capacitor 9, and the charge / discharge capacitor 9 shows an inter-terminal voltage Vcf. In a steady state, the inter-terminal voltage Vcf of the charge / discharge capacitor 9 is controlled to be about ½ of the output voltage Vout, and the input voltage Vin, output voltage Vout, and terminals of the charge / discharge capacitor 9 are controlled. The magnitude relationship of the inter-voltage Vcf is as follows.

  Vout> Vcf> Vin

  In the state where the gate signal of the switching element 5 is High and the gate signal of the switching element 6 is High (mode 4), both the switching elements 5 are turned on. Therefore, energy is transferred from the DC power source 1 to the reactor 2 through the following path. To do.

  DC power source 1 → reactor 2 → switching element 6 → switching element 5

  Next, when the gate signal of the switching element 5 is high and the gate signal of the switching element 6 is low (mode 1), the switching element 5 is turned on and the switching element 6 is turned off. The accumulated energy is superimposed on the DC power source 1 and transferred to the charge / discharge capacitor 9.

  DC power source 1 → reactor 2 → diode 7 → charge / discharge capacitor 9 → switching element 5

  Next, in the state where the gate signal of the switching element 5 is High and the gate signal of the switching element 6 is High (mode 4), the switching elements 5 and 6 are both turned on. Energy shifts to 2.

  DC power source 1 → reactor 2 → switching element 6 → switching element 5

  Next, when the gate signal of the switching element 5 is Low and the gate signal of the switching element 6 is High (mode 2), the switching element 5 is turned off and the switching element 6 is turned on. The energy accumulated in the charge / discharge capacitor 9 is superimposed on the DC power source 1 and transferred to the voltage dividing capacitors 10 and 11.

  DC power source 1 → reactor 2 → switching element 6 → charge / discharge capacitor 9 → diode 8 → voltage dividing capacitor 11 → voltage dividing capacitor 10

  By repeating the series of operations described above, the input voltage Vin input between the VL terminal and the Vcom terminal is boosted to an arbitrary voltage more than twice, and is output as the output voltage Vout between the VH terminal and the Vcom terminal.

  Next, the operation when the input voltage Vin is applied between the VL terminal and the Vcom terminal when the DC / DC power converter stops normal operation and the switching elements 5 and 6 are in the control stop state is shown in FIG. This will be described with reference to FIG. FIG. 5 is a diagram illustrating a current path when an input voltage is applied in a control stop state of the DC / DC power converter according to the embodiment.

  If the input voltage Vin is applied between the VL terminal and the Vcom terminal when the switching elements 5 and 6 are both in the control stop state and the switching elements 5 and 6 are in the off state, the first voltage equalization is performed. When there is no path including the diode 12, the first voltage equalizing Zener diode 13, and the second current limiting resistor 14, the input voltage Vin is applied to the smoothing capacitor 4, and the output voltage Vout is the input voltage Vin. However, the charge / discharge capacitor 9 discharges due to its own internal ESR and the leakage current of each switching element 6 and diode 7.

  At this time, when the voltage between the terminals of the charge / discharge capacitor 9 decreases to almost zero, the smoothing capacitor 4 and the switching element 5 are connected in parallel, and the voltage of the smoothing capacitor 4 at this time, that is, the input voltage Vin. A voltage substantially equal to is applied between the drain and source of the switching element 5.

  On the other hand, in the DC / DC power converter according to the embodiment having a path including the first voltage equalizing diode 12, the first voltage equalizing Zener diode 13, and the first current limiting resistor 14, FIG. As shown in FIG. 5, the charge / discharge capacitor 9 and the voltage dividing capacitors 10 and 11 are charged by the current flowing through the following two paths.

Path 1:
VL terminal-> reactor 2-> diode 7-> diode 8-> voltage dividing capacitor 11-> voltage dividing capacitor 10-> Vcom terminal

Path 2:
VL terminal → reactor 2 → diode 7 → charge / discharge capacitor 9 → first voltage equalizing diode 12 → first voltage equalizing Zener diode 13 → first current limiting resistor 14 → voltage dividing capacitor 10 → Vcom terminal

  Thereby, the input voltage Vin is divided and applied to the connection body of the charge / discharge capacitor 9 and the voltage dividing capacitor 11 connected in parallel to each other and the voltage dividing capacitor 10 connected in series to the connection body. It becomes.

  Here, the relationship between the capacitance value Cf of the charging / discharging capacitor 9, the capacitance value Co1 of the voltage dividing capacitor 10, and the capacitance value Co2 of the voltage dividing capacitor 11 satisfies Cf << Co1 = Co2, and the forward voltage of the diodes 7 and 8; Assuming that the breakdown voltage of the first voltage equalizing Zener diode 13 and the current flowing through the first current limiting resistor 14 are sufficiently small, the voltage applied between the drain and the source of the switching element 5 is Vds1, and the switching element 6 Assuming that the voltage applied between the drain and the source is Vds2, the relationship between the voltage Vco1 between the terminals of the voltage dividing capacitor 10, the voltage Vco2 between the terminals of the voltage dividing capacitor 11, and the voltage Vcf between the terminals of the charge / discharge capacitor 9 is It becomes as follows.

Vco1≈Vco2≈Vin / 2
Vco1≈Vds1
Vcf≈Vds2≈Vin / 2

  That is, even when the input voltage Vin is applied between the VL terminal and the Vcom terminal when the switching elements 5 and 6 are in the control stop state and the switching elements 5 and 6 are both in the off state, the first voltage equalization is performed. By providing the rectifying diode 12, the imbalance between the terminal voltage Vcf of the charge / discharge capacitor 9 and the terminal voltages Vco 2, Vco 1 of the voltage dividing capacitors 10, 11 can be eliminated, and the drains of the switching elements 5, 6 can be eliminated. -The voltages Vds1 and Vds2 applied between the sources are both substantially equalized to Vin / 2.

  Next, when the DC / DC power converter stops normal operation and the switching elements 5 and 6 are in the control stop state, the DC power source 1 is in a state where the voltage remains in the charge / discharge capacitor 9 and the smoothing capacitor 4. 6, that is, the operation when the voltage between the VL terminal and the Vcom terminal is drastically reduced to zero or near zero (hereinafter referred to as “input voltage sudden drop”) will be described with reference to FIG. 6.

  FIG. 6 is a diagram illustrating a current path when the input voltage suddenly decreases in the control stop state of the DC / DC power converter according to the embodiment. Moreover, FIG. 7 is a figure which shows transition of each part voltage when the input voltage sudden fall generate | occur | produces in the control stop state of the conventional DC / DC power converter device. Moreover, FIG. 8 is a figure which shows transition of each part voltage when the input voltage sudden reduction generate | occur | produces in the control stop state of the DC / DC power converter device concerning Embodiment. 7 and 8, the voltage applied between the drain and source of the switching element 5 is Vds1, the voltage applied between the drain and source of the switching element 6 is Vds2, and the reverse voltage of the diode 7 is used. Is Vd1, and the reverse voltage of the diode 8 is Vd2.

  When the switching elements 5 and 6 are both in the control stop state and the switching elements 5 and 6 are in the OFF state, if the input voltage suddenly decreases, the second voltage equalizing diode 15 and the second voltage When there is no path including the equalizing Zener diode 16 and the second current limiting resistor 17, the charge / discharge capacitor 9 is discharged by its own internal ESR and the leakage current of each switching element 6 and the diode 7.

  At this time, the voltage dividing capacitors 10 and 11 are also discharged in the same manner as the charging / discharging capacitor 9. However, as described above, when Cf << Co1 = Co2, the voltage dividing capacitors 10 and 11 are discharged. However, the charging / discharging capacitor 9 is rapidly discharged. At this time, when the voltage between the terminals of the charge / discharge capacitor 9 decreases to almost zero, the smoothing capacitor 4 and the diode 8 are connected in parallel, and the voltage of the smoothing capacitor 4 at this time is transiently applied to the diode 8. Applied.

  For example, when the step-up ratio N in the steady state is set to double, when the input voltage Vin is about 400V, the output voltage Vout is about 800V. Here, when the normal operation is stopped from the steady state, and the input voltage suddenly decreases at this point, the voltage of the smoothing capacitor 4 remains the output voltage value in the steady state, that is, a voltage of about 800V. .

  Therefore, in a conventional DC / DC power converter having no path including the second voltage equalizing diode 15, the second voltage equalizing Zener diode 16, and the second current limiting resistor 17, as shown in FIG. In addition, a voltage close to the output voltage value in the steady state (about 750 V in the example shown in FIG. 7) is applied to the diode 8 along with the discharge of the charge / discharge capacitor 9.

  On the other hand, in the DC / DC power conversion apparatus according to the embodiment having a path including the second voltage equalizing diode 15, the second voltage equalizing Zener diode 16, and the second current limiting resistor 17, the DC / DC power conversion apparatus according to the embodiment shown in FIG. As shown in FIG. 5, when a current flows through the following path, the charge of the voltage dividing capacitor 10 moves to the charge / discharge capacitor 9 and the charge / discharge capacitor 9 is charged.

  Voltage dividing capacitor 10 → second voltage equalizing Zener diode 16 → second current limiting resistor 17 → second voltage equalizing diode 15 → charge / discharge capacitor 9 → switching element 6 → reactor 2 → VL terminal → Vcom Terminal

  Thereby, the voltage of the smoothing capacitor 4 is divided and applied to a connection body of the charge / discharge capacitor 9 and the voltage dividing capacitor 10 connected in parallel to each other and a voltage dividing capacitor 11 connected in series to the connection body. Will be.

  Here, the relationship between the capacitance value Cf of the charging / discharging capacitor 9, the capacitance value Co1 of the voltage dividing capacitor 10, and the capacitance value Co2 of the voltage dividing capacitor 11 satisfies Cf << Co1 = Co2, and the second voltage equalizing Zener diode. Assuming that the breakdown voltage of 16 and the current flowing through the second current limiting resistor 17 are sufficiently small, the voltage Vco1 between the terminals of the voltage dividing capacitor 10, the voltage Vco2 between the terminals of the voltage dividing capacitor 11, and the terminals of the charge / discharge capacitor 9 The relationship among the voltage Vcf, the reverse voltage Vd1 of the diode 7, and the reverse voltage Vd2 of the diode 8 is as follows.

Vco1≈Vco2≈Vout / 2
Vcol≈Vcf + Vds1
Vd1≈Vcf−Vds2
Vd2≈Vco2≈Vco1≈Vcf + Vds1

  That is, the second voltage equalizing diode 15 is provided even when the input voltage suddenly drops when each of the switching elements 5 and 6 is in the control stop state and both the switching elements 5 and 6 are in the off state. Thus, the imbalance between the inter-terminal voltage Vcf of the charge / discharge capacitor 9 and the inter-terminal voltages Vco2, Vco1 of the voltage dividing capacitors 10, 11 can be eliminated, and the reverse voltage Vd2 of the diode 8 is an abbreviation of the output voltage Vout. 1/2.

  Therefore, in the DC / DC power converter according to the embodiment including the path including the second voltage equalizing diode 15, the second voltage equalizing Zener diode 16, and the second current limiting resistor 17, each switching is performed. If the input voltage suddenly drops when the elements 5 and 6 are in the control stop state and the switching elements 5 and 6 are both off, the charge / discharge capacitor 9 is rapidly discharged as shown in FIG. Without being applied, a voltage that is ½ or less of the output voltage value in the steady state (about 400 V in the example shown in FIG. 8) is applied to the diode 8, and then gradually decreases according to the discharge of the smoothing capacitor 4. Go.

  Next, the effect and operation of providing the first voltage equalizing Zener diode 13 and the second voltage equalizing Zener diode 16 will be described. As described above, in the present embodiment, the first voltage equalizing diode 12 and the second voltage equalizing diode 15 are connected to the first voltage equalizing Zener diode 13 and the second voltage equalizing diode 13, respectively. Zener diodes 16 are connected in reverse series.

  As described above, in the steady state during normal operation, the charge / discharge capacitor 9 repeats charge / discharge in order to perform the boosting operation. At this time, in the case where the first voltage equalizing Zener diode 13 is not provided, the potential of the negative terminal of the charge / discharge capacitor 9 is changed in the process of repeating the charge / discharge capacitor 9, 11 becomes higher than the potential at the connection point 11, current flows to the voltage dividing capacitor 10 via the first voltage equalizing diode 12, and the voltage dividing capacitor 10 is charged more than the voltage dividing capacitor 11. The voltage Vco1 between the terminals of the voltage capacitor 10 becomes larger than the voltage Vco2 between the terminals of the voltage divider capacitor 11, voltage imbalance between the voltage divider capacitor 10 and the voltage divider capacitor 11 occurs, and the operation becomes unstable.

  Therefore, the first voltage equalizing Zener diode 13 is inserted in reverse series with the first voltage equalizing diode 12 so that the switching elements 5 and 6 can be input between the VL terminal and the Vcom terminal in the control stop state. In the steady state, the potential of the negative side terminal of the charge / discharge capacitor 9 is set to the voltage dividing capacitor while suppressing the occurrence of voltage imbalance of the voltage dividing capacitors 10 and 11 when the voltage Vin is applied to ensure stable operation of the device. By preventing the potential from being higher than the potential at the connection point of 10 and 11, the occurrence of voltage imbalance in the voltage dividing capacitors 10 and 11 is suppressed, and the stable operation of the device is ensured. Hereinafter, the operation and effect when the first voltage equalizing Zener diode 13 is provided will be described.

  First, the case where the input voltage Vin is applied between the VL terminal and the Vcom terminal in the control stop state of the switching elements 5 and 6 will be described.

  As described above, when the switching elements 5 and 6 are in the control stop state, the switching elements 5 and 6 are both turned off. At this time, when the input voltage Vin is applied between the VL terminal and the Vcom terminal, As shown in FIG. 5, the first voltage equalizing Zener diode 13 conducts and current flows through the following two paths, whereby the charge / discharge capacitor 9 and the voltage dividing capacitors 10 and 11 are charged.

Path 1:
VL terminal-> reactor 2-> diode 7-> diode 8-> voltage dividing capacitor 11-> voltage dividing capacitor 10-> Vcom terminal

Path 2:
VL terminal → reactor 2 → diode 7 → charge / discharge capacitor 9 → first voltage equalizing diode 12 → first voltage equalizing Zener diode 13 → first current limiting resistor 14 → voltage dividing capacitor 10 → Vcom terminal

  As a result, the input voltage Vin is connected to the connecting body of the charge / discharge capacitor 9 and the voltage dividing capacitor 10 connected in parallel to each other via the first voltage equalizing Zener diode 13, and to the connecting body in series. The voltage is applied to the voltage capacitor 11.

  Here, the relationship between the capacitance value Cf of the charging / discharging capacitor 9, the capacitance value Co1 of the voltage dividing capacitor 10, and the capacitance value Co2 of the voltage dividing capacitor 11 satisfies Cf << Co1 = Co2, and the first voltage equalizing Zener diode. 13 is Vfzd, the voltage Vco1 between the terminals of the voltage dividing capacitor 10, the voltage Vco2 between the terminals of the voltage dividing capacitor 11, the voltage Vcf between the terminals of the charge / discharge capacitor 9, the reverse voltage Vd1 of the diode 7, the diode The relationship of the reverse voltage Vd2 of 8 is as follows.

Vco1≈Vco2≈Vin / 2
Vcf≈Vds2≈Vin / 2−Vfzd
Vds1≈Vin / 2 + Vfzd

  That is, even if the first voltage equalizing Zener diode 13 is inserted in reverse series with the first voltage equalizing diode 12, the switching elements 5 and 6 are in the control stop state, and the switching elements 5 and 6 are not controlled. When the input voltage Vin is applied between the VL terminal and the Vcom terminal when both are in the off state, the first voltage equalizing Zener diode 13 becomes conductive, so that the terminals of the charge / discharge capacitor 9 are connected. The imbalance between the voltage Vcf and the terminal voltages Vco2 and Vco1 of the voltage dividing capacitors 10 and 11 can be eliminated, and the voltages Vds1 and Vds2 applied between the drain and source of the switching elements 5 and 6 can be substantially equalized. .

  Next, a description will be given of the case of a steady state in which the switching elements 5 and 6 are on / off controlled and the output voltage is stably obtained.

  First, in mode 2 in which the switching element 5 is turned off and the switching element 6 is turned on in a steady state, the sum of the inter-terminal voltage Vcf of the charge / discharge capacitor 9 and the breakdown voltage Vfzd of the first voltage equalizing Zener diode 13 is added. The current path changes depending on the magnitude of the value and the voltage Vco2 between the terminals of the voltage dividing capacitor 11.

  In order to prevent the voltage imbalance of the voltage dividing capacitors 10 and 11 from occurring, the first voltage equalizing Zener diode 13 is turned off, that is, the voltage Vcf between the terminals of the charge / discharge capacitor 9 and the first voltage The sum of the voltage equalization Zener diode 13 and the breakdown voltage Vfzd may be larger than the voltage Vco2 between the terminals of the voltage dividing capacitor 11, that is, Vcf + Vfzd ≧ Vco2. The current path at this time is as follows.

  DC power source 1 → reactor 2 → switching element 6 → charge / discharge capacitor 9 → diode 8 → voltage dividing capacitor 11 → voltage dividing capacitor 10

  Further, in the mode 3 in which the switching elements 5 and 6 are both turned off in the steady state, the sum of the voltage Vcf between the terminals of the charge / discharge capacitor 9 and the breakdown voltage Vfzd of the first voltage equalizing Zener diode 13 The current path changes depending on the magnitude relationship with the inter-terminal voltage Vco2 of the voltage dividing capacitor 11.

  In order to prevent the voltage imbalance of the voltage dividing capacitors 10 and 11 from occurring, the first voltage equalizing Zener diode 13 is turned off, that is, the voltage Vcf between the terminals of the charge / discharge capacitor 9 and the first voltage The sum of the voltage equalization Zener diode 13 and the breakdown voltage Vfzd may be larger than the voltage Vco2 between the terminals of the voltage dividing capacitor 11, that is, Vcf + Vfzd ≧ Vco2. The current path at this time is as follows.

  DC power source 1 → reactor 2 → diode 7 → diode 8 → voltage dividing capacitor 11 → voltage dividing capacitor 10

  Therefore, in order to prevent unstable operation in the mode 2 and mode 3 in the steady state, the minimum value of the voltage between the terminals of the charge / discharge capacitor 9 is Vcf (min), and the maximum value of the voltage between the terminals of the voltage dividing capacitor 11 is set. When Vco2 (max) is set, the breakdown voltage Vfzd of the first voltage equalizing Zener diode 13 may be set to a value satisfying the following relationship.

  Vfzd ≧ Vco2 (max) −Vcf (min)

  If the second voltage equalizing Zener diode 16 is not provided, the charging / discharging capacitor 9 repeats charging / discharging in a steady state during normal operation. When the potential becomes lower than the potential at the connection point of the voltage dividing capacitors 10 and 11, current flows from the voltage dividing capacitor 10 via the second voltage equalizing diode 15, and the voltage dividing capacitor 10 is discharged. The voltage Vco1 between the terminals of the voltage capacitor 10 becomes larger than the voltage Vco2 between the terminals of the voltage divider capacitor 11, voltage imbalance between the voltage divider capacitor 10 and the voltage divider capacitor 11 occurs, and the operation becomes unstable.

  Therefore, when the second voltage equalizing Zener diode 16 is inserted in reverse series with the second voltage equalizing diode 15, thereby causing a sudden drop in the input voltage when the switching elements 5 and 6 are stopped. In the steady state, the potential of the negative-side terminal of the charge / discharge capacitor 9 is at the connection point of the voltage dividing capacitors 10 and 11 while suppressing the occurrence of voltage imbalance of the voltage dividing capacitors 10 and 11 and ensuring stable operation of the device. By preventing the voltage from becoming lower than the potential, the occurrence of voltage imbalance in the voltage dividing capacitors 10 and 11 is suppressed to ensure stable operation of the device. Hereinafter, an operation and an effect when the second voltage equalizing Zener diode 16 is provided will be described.

  First, a description will be given of a case where a sudden drop in the input voltage occurs in the control stop state of the switching elements 5 and 6.

  When each of the switching elements 5 and 6 is in the control stop state, both of the switching elements 5 and 6 are off, and when a sudden drop in the input voltage occurs at this time, as shown in FIG. When the Zener diode 16 becomes conductive and a current flows through the following path, the charge of the voltage dividing capacitor 10 moves to the charge / discharge capacitor 9 and the charge / discharge capacitor 9 is charged.

  Voltage dividing capacitor 10 → second voltage equalizing Zener diode 16 → second current limiting resistor 17 → second voltage equalizing diode 15 → charge / discharge capacitor 9 → switching element 6 → reactor 2 → VL terminal → Vcom Terminal

  Thereby, the voltage of the smoothing capacitor 4 is divided and applied to a connection body of the charge / discharge capacitor 9 and the voltage dividing capacitor 10 connected in parallel to each other and a voltage dividing capacitor 11 connected in series to the connection body. Will be.

  Here, the relationship between the capacitance value Cf of the charging / discharging capacitor 9, the capacitance value Co1 of the voltage dividing capacitor 10, and the capacitance value Co2 of the voltage dividing capacitor 11 satisfies Cf << Co1 = Co2, and the second voltage equalizing Zener diode. When the breakdown voltage of 16 is Vhzd, the voltage Vco1 between the terminals of the voltage dividing capacitor 10, the voltage Vco2 between the terminals of the voltage dividing capacitor 11, the voltage Vcf between the terminals of the charge / discharge capacitor 9, the reverse voltage Vd1 of the diode 7, the diode The relationship of the reverse voltage Vd2 of 8 is as follows.

Vco1≈Vco2≈Vout / 2
Vcol≈Vcf + Vds1
Vd1≈Vcf−Vds2
Vd2≈Vco2 + Vhzd≈Vco1 + Vhzd≈Vcf + Vds1 + Vhzd

  That is, even if the second voltage equalizing Zener diode 16 is inserted in reverse series with the second voltage equalizing diode 15, the switching elements 5 and 6 are in the control stop state, and the switching elements 5 and 6 are not controlled. When the input voltage suddenly decreases when both 6 are OFF, the second voltage equalizing Zener diode 16 is turned on, so that the voltage Vcf between the terminals of the charge / discharge capacitor 9 and each voltage dividing capacitor The unbalance of the inter-terminal voltages Vco2 and Vco1 of 10 and 11 can be eliminated, and the reverse voltage Vd2 of the diode 8 can be made approximately ½ of the output voltage Vout.

  Next, a description will be given of the case of a steady state in which the switching elements 5 and 6 are on / off controlled and the output voltage is stably obtained.

  First, in the steady state, in mode 1 in which the switching element 5 is on and the switching element 6 is off, the sum of the voltage Vco1 between the terminals of the voltage dividing capacitor 10 and the breakdown voltage Vhzd of the second voltage equalizing Zener diode 13 is added. The current path changes depending on the magnitude of the value and the voltage Vcf between the terminals of the charge / discharge capacitor 9.

  In order to prevent the voltage imbalance of the voltage dividing capacitors 10 and 11 from occurring, the second voltage equalizing Zener diode 16 is turned off, that is, the voltage Vco1 between the terminals of the voltage dividing capacitor 10 and the second voltage The sum of the breakdown voltage Vhzd of the voltage equalizing Zener diode 13 and the voltage Vcf between terminals of the charge / discharge capacitor 9 may be set to be larger, that is, Vco1 + Vhzd ≧ Vcf. The current path at this time is as follows.

  DC power source 1 → reactor 2 → diode 7 → charge / discharge capacitor 9 → switching element 5

  Further, even in the mode 4 in which the switching elements 5 and 6 are both turned on in the steady state, the sum of the inter-terminal voltage Vco1 of the voltage dividing capacitor 10 and the breakdown voltage Vhzd of the second voltage equalizing Zener diode 13 And the current path changes depending on the magnitude relationship between the inter-terminal voltage Vcf of the charge / discharge capacitor 9.

  In order to prevent the voltage imbalance of the voltage dividing capacitors 10 and 11 from occurring, the second voltage equalizing Zener diode 16 is turned off, that is, the voltage Vco1 between the terminals of the voltage dividing capacitor 10 and the second voltage The sum of the breakdown voltage Vhzd of the voltage equalizing Zener diode 13 and the voltage Vcf between terminals of the charge / discharge capacitor 9 may be set to be larger, that is, Vco1 + Vhzd ≧ Vcf. The current path at this time is as follows.

  DC power source 1 → reactor 2 → switching element 6 → switching element 5

  Therefore, in order to prevent unstable operation in the mode 1 and mode 4 in the steady state, the maximum value of the inter-terminal voltage of the charge / discharge capacitor 9 is Vcf (max), and the minimum inter-terminal voltage of the voltage dividing smoothing capacitor 10 is set. When the value Vco1 (min) is set, the breakdown voltage Vhzd of the second voltage equalizing Zener diode 16 may be set to a value satisfying the following relationship.

  Vhzd ≧ Vcf (max) −Vco1 (min)

  As described above, in the DC / DC power converter according to the embodiment, the voltage Vcf between the terminals of the charge / discharge capacitor 9 and the voltage Vco2, between the terminals of the voltage dividing capacitors 10 and 11, regardless of the steady state / control stop state. Since the voltage applied to Vco1 can be made substantially equal, not only the charging / discharging capacitor 9 and the voltage dividing capacitors 10 and 11, but also the switching elements 5 and 6 and the diodes 7 and 8 constituting the DC voltage conversion unit 3. The breakdown voltage of each component such as can be further reduced.

  Here, an effect and an operation by providing the first current limiting resistor 14 and the second current limiting resistor 17 will be described.

  As described above, the first voltage equalizing diode 12 is connected by connecting the first current limiting resistor 14 in series with the first voltage equalizing diode 12 and the first voltage equalizing Zener diode 13. The current flowing through the first voltage equalizing Zener diode 13 is limited.

  Further, by connecting the second current limiting resistor 17 in series with the second voltage equalizing diode 15 and the second voltage equalizing Zener diode 16, the second voltage equalizing diode 15 and the second voltage equalizing diode 15 and the second voltage equalizing diode 15 are connected. The current flowing through the voltage equalizing Zener diode 16 is limited.

  By adopting such a configuration, the switching elements 5 and 6 in the steady state can be instantaneously turned on / off, at the time of transition from the steady state to the control stop state, or when the DC power supply 1 is suddenly lowered. Current flows through the first voltage equalizing diode 12, the first voltage equalizing Zener diode 13, the second voltage equalizing diode 15, and the second voltage equalizing Zener diode 16. Therefore, it is possible to improve the reliability of the DC / DC power converter according to the present embodiment.

  FIG. 9 is a diagram illustrating an example in which the DC / DC power converter according to the embodiment is connected to a load. As a load connected to the DC / DC power converter according to the embodiment, for example, a DC load may be used, and single-phase AC power is supplied to the subsequent stage of the DC / DC power converter via a single-phase inverter. It may be a supplied single-phase AC load. Alternatively, it may be a three-phase AC load in which three-phase AC power is supplied via a three-phase inverter to the subsequent stage of the DC / DC power converter.

  The DC / DC power converter according to the above-described embodiment can also be used as a DC / DC power converter connected to a single-phase or three-phase power system. FIG. 10 is a diagram illustrating an example in which the DC / DC power converter according to the embodiment is connected to a single-phase or three-phase power system.

  As a typical use example of such a configuration, for example, a DC / DC power conversion device incorporated in a power conditioner for a photovoltaic power generation system can be considered. When the DC / DC power converter according to the embodiment is used for a power conditioner for a solar power generation system, a solar cell string in which a plurality of solar cell modules are connected in series as a DC power source 1, or a solar cell string is connected in parallel The connected solar cell array is connected to the power system via an inverter.

  In the conventional configuration, the withstand voltage of each component of the DC voltage conversion unit, the voltage dividing capacitor constituting the charge / discharge capacitor and the smoothing capacitor, etc. must be set to a withstand voltage value in consideration of the maximum output voltage of the DC / DC power converter. Therefore, when it is applied as a DC / DC power conversion device incorporated in a power conditioner for a photovoltaic power generation system in which both Vin and Vout are high voltages, the influence on cost and efficiency is large.

  In the DC / DC power converter according to the present embodiment, as described above, the inter-terminal voltage Vcf of the charge / discharge capacitor 9 and the inter-terminal voltages of the voltage dividing capacitors 10 and 11 are independent of the steady state / control stop state. Since the voltages applied to Vco2 and Vco1 can be made substantially equal, not only the charging / discharging capacitor 9 and the voltage dividing capacitors 10 and 11, but also the switching elements 5 and 6 and the diode 7 constituting the DC voltage conversion unit 3 are used. , 8 etc., the breakdown voltage of each component can be further reduced.

  Further, in the case of a photovoltaic power generation system, there may frequently be a situation where the input voltage of the DC / DC power converter greatly decreases to zero or near zero due to the sun suddenly hiding in the clouds and the sun setting. . Including this, the DC / DC power converter according to the present embodiment is suitable for use in a power conditioner for photovoltaic power generation.

  As described above, according to the DC / DC power converter and the power conditioner for the photovoltaic power generation system according to the embodiment, a reactor connected to the DC power supply, and a plurality of switching elements connected to the reactor, A DC voltage converter having a charge / discharge capacitor that is charged / discharged by turning on / off of the switching element, a plurality of diodes that provide a charging path and a discharging path of the charge / discharge capacitor, and a DC voltage converter connected to the DC voltage converter In the configuration including the output-side smoothing capacitor having a plurality of voltage-dividing capacitors connected in series to each other, the first voltage equalization that allows current to flow from the negative-side terminal of the charge / discharge capacitor to the mutual connection point of each voltage-dividing capacitor And a first voltage equalization connected in reverse series with the first voltage equalization diode. A Zener diode, a second voltage equalizing diode that allows current to flow from the connection point of each voltage dividing capacitor to the positive terminal of the charge / discharge capacitor, and the second voltage equalizing diode are connected in anti-series. By providing the second voltage equalizing Zener diode, the voltage applied to the inter-terminal voltage of the charge / discharge capacitor and the inter-terminal voltage of each voltage dividing capacitor is substantially equal regardless of the steady state / control stop state. Therefore, not only the charge / discharge capacitor and each voltage dividing capacitor, but also the breakdown voltage of each component such as a switching element and a diode constituting the DC voltage converter can be reduced, and the cost is high and the efficiency is high. A DC / DC power conversion device and a solar power generation system can be obtained.

  Also, a first current limiting resistor that limits a current flowing through the first voltage equalizing diode and the first voltage equalizing Zener diode, and a second voltage equalizing diode and a second voltage equalizing By providing a second current limiting resistor that limits the current flowing through the zener diode for switching, the switching element in the steady state is controlled to be turned on / off, the transition from the steady state to the control stop state, or the DC power supply suddenly decreases. Momentary transient current at the time of the occurrence of the first voltage equalizing diode, the first voltage equalizing Zener diode, the second voltage equalizing diode, and the second voltage equalizing Zener diode. The DC / DC power converter according to the embodiment and the power condition for the solar power generation system can be controlled. It is possible to improve the reliability.

  Note that the configuration shown in the above embodiment is an example of the configuration of the present invention, and can be combined with another known technique, and a part thereof is omitted without departing from the gist of the present invention. Needless to say, it is possible to change the configuration.

  DESCRIPTION OF SYMBOLS 1 DC power supply, 2 Reactor, 3 DC voltage conversion part, 4 Smoothing capacitor, 5, 6 Switching element, 7, 8 Diode, 9 Charging / discharging capacitor, 10, 11 Voltage dividing capacitor, 12 1st voltage equalization diode, 13 first voltage equalizing Zener diode, 14 first current limiting resistor, 15 second voltage equalizing diode, 16 second voltage equalizing Zener diode, 17 second current limiting resistor.

Claims (4)

A reactor connected to a DC power supply;
DC voltage conversion having a plurality of switching elements connected to the reactor, a charging / discharging capacitor that is charged / discharged by turning on / off the switching element, and a plurality of diodes that provide a charging path and a discharging path of the charging / discharging capacitor And
A smoothing capacitor on the output side, which is connected to the DC voltage conversion unit and has a plurality of voltage dividing capacitors connected in series with each other;
A first voltage equalizing diode that is forward-connected in a direction in which a current flows from a negative electrode side terminal of the charge / discharge capacitor to a connection point of the voltage dividing capacitors;
A first voltage equalizing Zener diode connected in anti-series with the first voltage equalizing diode;
A second voltage equalizing diode that is sequentially connected in a direction in which a current flows from a connection point of the voltage dividing capacitors to a positive terminal of the charge / discharge capacitor;
A second voltage equalizing Zener diode connected in anti-series with the second voltage equalizing diode;
A DC / DC power conversion device comprising:   2. The DC / DC power conversion according to claim 1, further comprising a first current limiting resistor that limits a current flowing through the first voltage equalizing diode and the first voltage equalizing Zener diode. apparatus.   3. The DC / DC according to claim 1, further comprising a second current limiting resistor configured to limit a current flowing through the second voltage equalizing diode and the second voltage equalizing Zener diode. Power conversion device.   A power conditioner for a photovoltaic power generation system, comprising the DC / DC power converter according to any one of claims 1 to 3.

Images