WO2012140781A1

WO2012140781A1 - Dc/dc power conversion device and photovoltaic power generation system

Info

Publication number: WO2012140781A1
Application number: PCT/JP2011/059441
Authority: WO
Inventors: 一平竹内; 奥田　達也
Original assignee: 三菱電機株式会社
Priority date: 2011-04-15
Filing date: 2011-04-15
Publication date: 2012-10-18
Also published as: JPWO2012140781A1; JP5528622B2

Abstract

To provide a DC/DC power conversion device, and a photovoltaic power generation system, which are capable of boosting an output voltage of each of DC power sources to a desired direct current voltage, even when connecting a plurality of the DC power sources, the output voltages of which are different. The DC/DC power conversion device is provided with: a charge auxiliary capacitor (10) connected in series with a charge and discharge capacitor (7) by turning first and second switching elements (51, 52) off, and charged along with the charge and discharge capacitor (7) by energy stored in a reactor (4); a back flow preventing diode (8) preventing back flow of charges stored in the charge auxiliary capacitor (10); and a zener diode (9) connected in anti-series with the back flow preventing diode (8), and holding a voltage value of the charge auxiliary capacitor (10) within a constant range with respect to a connecting point of first and second output smoothing capacitors (11, 12). In this device, normal drive control for converting an input voltage to a desired output voltage is performed, and charge drive control for charging the charge and discharge capacitor (7) is performed when a voltage between both ends of the charge and discharge capacitor (7) is less than a predetermined voltage.

Description

DC / DC power converter and solar power generation system

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

The conventional DC / DC power converter performs the voltage conversion from direct current to direct current by controlling the amount of energy stored in and discharged from the reactor using the on / off operation of the 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 Can be made almost even.

Japanese Patent Publication No. 6-67181

However, for example, in a solar cell module in which the number of solar cell modules connected in series is different, the output voltage may be significantly different for each solar cell module group. When the solar cell module groups having different output voltages are connected to a plurality of DC / DC power converters and the outputs of the DC / DC power converters are connected in parallel as described above, in the above conventional technique, the output voltage is The charging / discharging capacitor of the DC / DC power converter to which the small solar cell module group is connected may not be charged. In a no-load state or a transient state up to a steady state, the voltage may be boosted to a desired DC voltage. There was a problem that it was not possible.

The present invention has been made in view of the above, and is capable of boosting the output voltage of each DC power source to a desired DC voltage even when a plurality of DC power sources having different output voltages are connected. An object is to provide a power conversion device and a solar 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 supply, a plurality of switching elements connected in series for switching the output of the reactor, and a plurality of switching elements. A plurality of charge / discharge capacitors that are charged / discharged by switching of the switching elements, a plurality of diodes that provide a charge path and a discharge path of the charge / discharge capacitors, and a drive control unit that drives and controls the plurality of switching elements. A DC voltage conversion unit, and a plurality of output smoothing capacitors connected in series to smooth parallel outputs of the plurality of DC voltage conversion units, the DC voltage conversion unit by turning off a plurality of the switching elements It is connected in series with the charge / discharge capacitor, and the energy stored in the reactor A charging auxiliary capacitor that is charged together with the charging / discharging capacitor, a backflow prevention diode that prevents backflow of charges stored in the charging auxiliary capacitor, and a voltage value of the charging auxiliary capacitor that is connected in reverse series to the backflow prevention diode. And a Zener diode that maintains a certain range with respect to the connection points of the plurality of output smoothing capacitors, and the drive control unit performs normal drive control for converting the input voltage to a desired output voltage, and When the voltage across the charge / discharge capacitor is less than a predetermined voltage, charge drive control for charging the charge / discharge capacitor is performed.

According to the present invention, even when a plurality of DC power supplies having different output voltages are connected, the output voltage of each DC power supply can be boosted to a desired DC voltage.

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 an example of each switching state in a steady state of the DC voltage conversion unit according to the embodiment. FIG. 3 is a diagram illustrating an example of a state transition of each part waveform in a steady state of the DC voltage conversion unit according to the embodiment. FIG. 4 is a diagram illustrating a current path when an input voltage is applied in a control stop state of the DC voltage conversion unit according to the embodiment. FIG. 5 is a diagram illustrating an example of each switching state in the charge drive control of the DC voltage converter according to the embodiment.

Hereinafter, a DC / DC power converter and a photovoltaic power generation system according to an embodiment of the present invention will be described 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 includes a DC voltage converter 1a that boosts an input voltage Vina input between a DC power supply 2a and an input terminal VLa and a reference voltage terminal Vcom; A first output smoothing in which a DC voltage conversion unit 1b that boosts an input voltage Vinb input between an input terminal VLb and a reference voltage terminal Vcom from a DC power supply 2b is connected in parallel, and its parallel output is connected in series. Smoothed by the capacitor, the output voltage Vout is output between the output terminal VH and the reference voltage terminal Vcom. In addition, although the example shown in FIG. 1 has shown the example which connected two

DC voltage converters

1a and 1b in parallel, it is also possible to connect three or more DC voltage converters in parallel. Further, the DC voltage conversion unit 1a and the DC voltage conversion unit 1b are both configured by the same components, and a and b are added to the end of the reference numerals related to the respective components. In the case where it is not necessary to distinguish, the description will be made by omitting a and b at the end.

The DC voltage conversion unit 1 is connected between an input terminal VL and a reference voltage terminal Vcom, and has an input-side smoothing capacitor 3 that smoothes the input voltage Vin, and a reactor that has one end connected to the positive terminal of the input-side smoothing capacitor 3. 4, the first switching element 51 and the second switching element 52 connected in series between the other end of the reactor 4 and the reference voltage terminal Vcom, and the other end of the reactor 4 and the output terminal VH, One end is connected to the connection point of the first diode 61 and the second diode 62 connected in series in the forward direction from the input side to the output side, and the connection point of the first diode 61 and the second diode 62. The charge / discharge capacitor 7 having the other end connected to the connection point of the switching element 51 and the second switching element 52, the first switching element 51 and the second switching element 52 A backflow prevention diode 8 having an anode connected to a connection point between the switching element 52 and the charge / discharge capacitor 7, a charge auxiliary capacitor 10 connected between the cathode of the backflow prevention diode 8 and the reference voltage terminal Vcom, and a backflow Between the connection point of the prevention diode 8 and the auxiliary charge capacitor 10 and the connection point of the first output-side smoothing capacitor 11 and the second output-side smoothing capacitor 12, it is connected in reverse series to the backflow prevention diode 8. A Zener diode 9 and a drive control unit 100 that drives and controls the first switching element 51 and the second switching element 52 are provided. The backflow prevention diode 8 is connected to the first switching element 51 and the second switching element M from the connection point M between the first output-side smoothing capacitor 11 and the second output-side smoothing capacitor 12 when the first switching element 51 is turned on. The zener diode 9 has a function of preventing a current from flowing back to the connection point B of the switching element 52, and the Zener diode 9 flows from the point B to the point M when the second switching element 52 is turned on. And has a function of maintaining the voltage of the auxiliary charging capacitor 10 within a certain range. In the example shown in FIG. 1, MOSFETs are used as the first and second switching elements. However, power transistors such as IGBTs may be used.

The drive control unit 100 includes a charge necessity determination unit 13 that determines whether or not the charge / discharge capacitor 7 needs to be charged, and a drive pulse generation unit that generates a drive pulse for driving the first switching element 51 and the second switching element 52. 14. The drive pulse generation unit 14 includes a normal drive pulse generation unit 141 that generates a drive pulse for normal drive control, and a charge drive pulse generation unit 142 that generates a drive pulse for charge drive control.

Next, the operation in the steady state of the DC voltage converter 1 according to the embodiment will be described with reference to FIGS. FIG. 2 is a diagram illustrating an example of each switching state in a steady state of the DC voltage conversion unit according to the embodiment. Moreover, FIG. 3 is a figure which shows an example of the state transition of each part waveform in the steady state of the DC voltage converter concerning Embodiment. FIG. 3A shows an example when the boost ratio is less than twice, and FIG. 3B shows an example when the boost ratio is two times or more. The steady state refers to a state where the boosting operation is stably performed by normal drive control. In the example shown in FIG. 2, a and b at the end of the reference numerals are omitted.

As shown in FIG. 2, there are four switching states of the DC voltage conversion unit 1 in a steady state: state 1 to state 4. In the state 1, the first switching element 51 is turned on and the second switching element 52 is turned off, and energy is stored in the charge / discharge capacitor 7. In the state 2, the first switching element 51 is turned off and the second switching element 52 is turned on, and the energy of the charge / discharge capacitor 7 is released. In the state 3, both the first switching element 51 and the second switching element 52 are turned off, and the energy of the reactor 4 is released. In the state 4, both the first switching element 51 and the second switching element 52 are turned on, and energy is stored in the reactor 4. By appropriately setting the time ratios of these switching states and transitioning between the switching states, the input voltage Vin input between the input terminal VL and the reference voltage terminal Vcom is boosted to an arbitrary voltage, and the output terminal VH -An output voltage Vout can be output between the reference voltage terminals Vcom.

In the normal drive control in the steady state of the DC voltage converter 1 according to the embodiment, when the step-up ratio N of the output voltage Vout with respect to the input voltage Vin is less than twice (Vout / Vin = N <2: FIG. 3A). ) And the case of more than twice (Vout / Vin = N ≧ 2: FIG. 3B), the switching pattern is different.

First, the operation when the step-up ratio N is less than 2 will be described. In the steady state, the voltage Vcf across the charging / discharging capacitor 7 is controlled to be about a half of the output voltage Vout. The input voltage Vin, the output voltage Vout, and the terminal voltage Vcf of the charging / discharging capacitor 7 are controlled. The size relationship is as follows.

Vout> Vin> Vcf

First, in the state 1, when the gate signal G1 of the first switching element 51 becomes High and the gate signal G2 of the second switching element 52 becomes Low, the first switching element 51 is turned on and the second switching element 52 is turned on. Since it is turned off, energy is transferred from the input-side smoothing capacitor 3 to the reactor 4 through the following path, and further to the charge / discharge capacitor 7 through the first diode 61 (broken arrow in FIG. 2A).

Input-side smoothing capacitor 3 → reactor 4 → first diode 61
→ Charging / discharging capacitor 7 → first switching element 51

Next, when the state transits to the state 3 and the gate signal G1 of the first switching element 51 becomes Low and the gate signal G2 of the second switching element 52 becomes Low, the first switching element 51 is turned off and the second switching element 51 is turned off. Since the element 52 is turned off, the energy accumulated in the reactor 4 through the following path is superimposed on the input-side smoothing capacitor 3, and the first output-side smoothing is performed via the first diode 61 and the second diode 62. Transition is made to the capacitor 11 and the second output-side smoothing capacitor 12 (broken arrows in FIG. 2C).

Input-side smoothing capacitor 3 → reactor 4 → first diode 61
→ second diode 62 → second output-side smoothing capacitor 12
→ first output smoothing capacitor 11

Next, when the state transits to the state 2 and the gate signal G1 of the first switching element 51 becomes Low and the gate signal G2 of the second switching element 52 becomes High, the first switching element 51 is turned off and the second switching element 51 is turned off. Since the element 52 is turned on, the energy accumulated in the charge / discharge capacitor 7 through the following path is superimposed on the input-side smoothing capacitor 3, and the first output-side smoothing capacitor 11 and the second output are connected via the second diode 62. 2 and the energy is accumulated in the reactor 4 (broken arrows in FIG. 2B).

Input-side smoothing capacitor 3 → reactor 4 → second switching element 52
→ Charging / discharging capacitor 7 → Second diode 62
→ second output-side smoothing capacitor 12 → first output-side smoothing capacitor 11

By repeating a series of state transitions (switching pattern: FIG. 3A) with the above-described state 1 → state 3 → state 2 → state 3 as one cycle, the signal is input between the input terminal VL and the reference voltage terminal Vcom. The input voltage Vin is boosted to an arbitrary voltage from 1 to 2 and output as an output voltage Vout between the output terminal VH and the reference voltage terminal Vcom.

Next, the operation when the step-up ratio N is twice or more will be described. In the steady state, the voltage Vcf across the charge / discharge capacitor 7 is controlled to be about a half of the output voltage Vout, as in the case where the step-up ratio N is less than twice, and the input voltage Vin, The magnitude relationship between the output voltage Vout and the voltage Vcf across the charge / discharge capacitor 7 is as follows.

Vout> Vcf> Vin

First, in the state 4, when the gate signal G1 of the first switching element 51 is High and the gate signal G2 of the second switching element 52 is High, the first switching element 51 is turned on and the second switching element 52 is turned on. Since it is turned on, energy is transferred from the input-side smoothing capacitor 3 to the reactor 4 through the following path (broken line arrow in FIG. 2D).

Input-side smoothing capacitor 3 → reactor 4 → second switching element 52
→ first switching element 51

Next, when the state transitions to state 1 and the gate signal G1 of the first switching element 51 is High and the gate signal G2 of the second switching element 52 is Low, the first switching element 51 is turned on and the second switching element 51 is turned on. Since the element 52 is turned off, the energy accumulated in the reactor 4 through the following path is superimposed on the input-side smoothing capacitor 3 and transferred to the charge / discharge capacitor 7 via the first diode 61 (FIG. 2 (a ) Dashed arrow).

Next, when the state transitions to state 4 and the gate signal G1 of the first switching element 51 is High and the gate signal G2 of the second switching element 52 is High, the first switching element 51 is turned on and the second switching element 51 is turned on. Since the element 52 is turned on, energy is transferred from the input-side smoothing capacitor 3 to the reactor 4 through the following path (broken line arrow in FIG. 2D).

Next, when the state transits to the state 2 and the gate signal G1 of the first switching element 51 becomes Low and the gate signal G2 of the second switching element 52 becomes High, the first switching element 51 is turned off and the second switching element 51 is turned off. Since the element 52 is turned on, the energy accumulated in the reactor 4 and the charge / discharge capacitor 7 is superimposed on the input side smoothing capacitor 3 through the following path, and the first output side smoothing capacitor is passed through the second diode 62. 11 and the second output-side smoothing capacitor 12 (broken line arrows in FIG. 2B).

By repeating a series of state transitions (switching pattern: FIG. 3B) with the above-described state 4 → state 1 → state 4 → state 2 as one cycle, it is input between the input terminal VL and the reference voltage terminal Vcom. The input voltage Vin is boosted to an arbitrary voltage more than twice and output as an output voltage Vout between the output terminal VH and the reference voltage terminal Vcom.

Next, in the DC / DC power converter according to the embodiment, refer to FIG. 1, FIG. 4, and FIG. 5 for the operation until each

DC voltage converter

1a, 1b shifts from the control stop state to the steady state. To explain. The control stop state refers to, for example, a case where a control power source (not shown) to the drive control unit 100 is not in a standby state, or any abnormality occurs in each DC

voltage conversion unit

1a, 1b to prevent a spillover failure. In this case, the first switching element 51 and the second switching element 52 are not driven and controlled.

Here, for example, in the DC / DC power converter shown in FIG. 1, the input voltage Vina input from the DC power source 2a to the DC voltage converting unit 1a is set to 900 V, and the DC voltage converting unit 1b is input from the DC power source 2b. Assuming that the input voltage Vinb is 300 V, the input voltage Vinb (= 300 V) ≦ the output voltage Vout ≦ the input voltage Vina (= 900 V) in the control stop state.

First, the operation from the control stop state to the steady state in the case of the DC voltage conversion unit 1a in FIG. 1, that is, when the input voltage Vina ≧ the output voltage Vout will be described. FIG. 4 is a diagram illustrating a current path when an input voltage is applied in a control stop state of the DC voltage conversion unit according to the embodiment. Here, a description will be given by omitting a and b at the end of the reference numerals.

In the control stop state, when the input voltage Vin ≧ the output voltage Vout, as shown in FIG. 4, the first switching element 51 and the second switching element 52 are in the OFF state, so that the input terminal VL−reference A current flows through the following three paths between the voltage terminals Vcom, and the charge / discharge capacitors 7, the first output-side smoothing capacitor 11, and the second output-side smoothing capacitor 12 are charged.

First path (broken line arrow in FIG. 5):
Input terminal VL → input side smoothing capacitor 3 → reference voltage terminal Vcom
Second route (dashed line arrow in FIG. 5):
Input terminal VL → reactor 4 → first diode 61
→ second diode 62 → second output-side smoothing capacitor 12
→ first output side smoothing capacitor 11 → reference voltage terminal Vcom
Third route (two-dot chain arrow in FIG. 5):
Input terminal VL → reactor 4 → first diode 61 → charge / discharge capacitor 7
→ Backflow prevention diode 8 → Zener diode 9
→ first output side smoothing capacitor 11 → reference voltage terminal Vcom

As a result, the input voltage Vin is applied to the input-side smoothing capacitor 3, and at the same time, the connected body of the charge / discharge capacitor 7 and the second output-side smoothing capacitor 12 connected in parallel via the Zener diode 9, This is applied to the first output-side smoothing capacitor 11 connected in series to this connection body.

Here, if the capacitance value of the charge / discharge capacitor 7 is Cf, the capacitance value of the first output-side smoothing capacitor 11 is Co1, and the capacitance value of the second output-side smoothing capacitor 12 is Co2, for example, Cf << Co1 = In the case of Co2, the both-ends voltage Vco1 of the first output-side smoothing capacitor 11, the both-ends voltage Vco2 of the second output-side smoothing capacitor 12, and the both-ends voltage Vcf of the charge / discharge capacitor 7 are as follows.

Vco1≈Vco2≈Vin / 2
Vcf≈Vin / 2−Vdz
(Vdz is the reverse voltage of the Zener diode 9)

Here, for example, when Vin = 900V and Vdz = 40V, Vco1≈Vco2≈450V and Vcf≈410V.

Therefore, when the input voltage Vin ≧ Vout (for example, the DC voltage conversion unit 1a in FIG. 1), the charging / discharging capacitor 7 is charged in the control stop state, so that the normal drive control is performed from the control stop state. By doing so, it is possible to shift to a steady state.

Next, in the case of the DC voltage converter 1b in FIG. 1, that is, the operation from the control stop state to the steady state when the input voltage Vinb <the output voltage Vout is described. In this case as well, description will be made with a and b at the end of the reference numerals omitted.

In the control stop state, when the input voltage Vin ≦ the output voltage Vout, a reverse voltage is applied to the first diode 61, so that no current flows in the second path and the third path described above. The discharge capacitor 7 is not charged. Therefore, when the input voltage Vin ≦ the output voltage Vout (for example, the DC voltage converter 1b in FIG. 1), the input voltage Vin is boosted to a desired voltage value even if the normal drive control is performed from the control stop state. I can't.

In the DC voltage conversion unit 1 according to the present embodiment, a switching pattern is used to charge the charge / discharge capacitor 7 when the charge / discharge capacitor 7 is insufficiently charged before or after the start of normal drive control. However, charge drive control different from normal drive control is performed. Hereinafter, the charge drive control of the DC voltage converter 1 according to the embodiment will be described.

The charge necessity determination unit 13 receives the output voltage Vout, the voltage Vco1 across the first output-side smoothing capacitor, and the voltage Vcf across the charge / discharge capacitor 7, and is charged / discharged before or after the start of normal drive control. When the voltage Vcf across the capacitor 7 is less than a predetermined value obtained by subtracting the voltage Vco1 across the first output-side smoothing capacitor from the output voltage Vout and the reverse voltage Vdz of the Zener diode 9 held in advance, that is, When the expression (1) is satisfied, it is determined that the charge / discharge capacitor 7 needs to be charged, and a charge drive control command is output.

Vcf <Vout-Vco1-Vdz (1)

When the voltage Vcf across the charge / discharge capacitor 7 is equal to or higher than a predetermined value obtained by subtracting the voltage Vco1 across the first output-side smoothing capacitor from the output voltage Vout and the reverse voltage Vdz of the Zener diode held in advance. That is, when the following equation (2) is satisfied, a normal drive control command is output.

Vcf ≧ Vout−Vco1−Vdz (2)

The drive pulse generator 14 receives the input voltage Vin, the voltage Vcf across the charge / discharge capacitor, and either the normal drive control command or the charge drive control command, and when the charge drive control command is input, The charge drive pulse generator 142 generates each drive pulse for charge drive control, outputs the drive pulses to the first switching element 51 and the second switching element 52, and starts charge drive control.

FIG. 5 is a diagram illustrating an example of each switching state in the charge drive control of the DC voltage converter according to the embodiment.

As shown in FIG. 5, there are three switching states of state 1 to state 3 as the switching state of the DC voltage conversion unit 1 in the charge drive control. In the state 1, the first switching element 51 is turned on, the second switching element 52 is turned off, a current flows through the reactor 4 through the charge / discharge capacitor 7, and energy is stored in the reactor 4. In the state 2, both the first switching element 51 and the second switching element 52 are turned off, and the energy accumulated in the reactor 4 is transferred to the charge / discharge capacitor 7 and the charge auxiliary capacitor 10. In the state 3, both the first switching element 51 and the second switching element 52 are turned on, the current flowing through the reactor 4 is increased, and energy is stored in the reactor 4. The both-ends voltage Vcf of the charge / discharge capacitor 7 is charged by appropriately setting the conduction ratio of the first switching element 51 and the second switching element 52 in each of these switching states and transitioning each switching state.

In the charge drive control of the DC voltage conversion unit 1 according to the embodiment, when the voltage difference between the input voltage Vin and the voltage Vcf across the charge / discharge capacitor 7 is larger than 100V (Vin−Vcf> 100V), it is 100V or less. In the case (Vin−Vcf ≦ 100 V), the switching pattern is different. That is, when the voltage difference between the input voltage Vin and the voltage Vcf across the charge / discharge capacitor 7 is greater than 100V, the charge / discharge capacitor 7 is first charged, and the input voltage Vin and the voltage Vcf across the charge / discharge capacitor 7 are When the voltage difference is 100 V or less, the switching pattern is switched and charging is performed until the voltage across the charge / discharge capacitor 7 becomes Vin / 2.

First, the switching pattern when the voltage difference between the input voltage Vin and the voltage Vcf across the charge / discharge capacitor 7 is larger than 100V, that is, when Vin−Vcf> 100V will be described. In the switching pattern in this case, the value obtained by subtracting 100V from the input voltage Vin is larger than half of the output voltage Vout until Vcf≈Vin-100V, that is, Vin-100V> Vout / 2. In this case, the charge / discharge capacitor 7 is charged until Vcf≈Vout / 2.

First, in state 1, since the first switching element 51 is turned on and the second switching element 52 is turned off, current flows through the following path, and energy is accumulated in the reactor 4 (in FIG. 5A). Dashed arrows).

Next, a transition is made to state 2, and the first switching element 51 is turned off and the second switching element 52 is turned off. Therefore, current flows through the following path, and the energy accumulated in the reactor 4 is transferred to the charge / discharge capacitor 7. And it transfers to the charge auxiliary capacitor 10 (broken line arrow of FIG.5 (b)).

Input-side smoothing capacitor 3 → reactor 4 → first diode 61
→ Charging / discharging capacitor 7 → Backflow prevention diode 8 → Charging auxiliary capacitor 10

After that, when the reactor current flowing through the reactor 4 becomes zero, the state transitions to the state 1, and Vcf≈Vin−100V by repeating a series of state transitions (switching patterns) with the state 1 → the state 2 as one cycle described above. Alternatively, the charge / discharge capacitor 7 is charged until Vcf≈Vout / 2. Note that the voltage across the charging auxiliary capacitor 10 is maintained at Vco2 to Vco2 + Vdz by the Zener diode 9.

Next, a switching pattern when the voltage difference between the input voltage Vin and the voltage Vcf across the charge / discharge capacitor 7 is 100 V or less, that is, when Vin−Vcf ≦ 100 V is described. In the switching pattern in this case, the charge / discharge capacitor 7 is charged until Vcf≈Vout / 2.

First, in state 1, since the first switching element 51 is turned on and the second switching element 52 is turned off, when the terminal voltage on the high voltage side of the reactor 4 is larger than the voltage Vcf across the charge / discharge capacitor 7, Then, a current flows through the following path, and energy is accumulated in the reactor 4 (broken arrows in FIG. 5A).

Next, a transition is made to state 3, and the first switching element 51 is turned on and the second switching element 52 is turned on. Therefore, a current flows through the following path, and a current flowing through the reactor 4 increases. Energy is accumulated (broken line arrow in FIG. 5C).

Next, a transition is made to state 1, and the first switching element 51 is turned on and the second switching element 52 is turned off, so that the energy accumulated in the reactor 4 in mode 3 is increased, and the high-pressure side of the reactor 4 is increased. When the terminal voltage becomes larger than the voltage Vcf across the charge / discharge capacitor 7, current flows through the following path, and energy is further accumulated in the reactor 4 (broken arrows in FIG. 5A).

After that, when the reactor current flowing through the reactor 4 becomes zero, the state transitions to the state 1, and the above-described series of state transitions (switching patterns) with the state 1 → the state 3 → the state 1 → the state 2 as one cycle are repeated. The charge / discharge capacitor 7 is charged until Vcf≈Vout / 2.

In addition, the conduction ratio of the first switching element 51 in the above-described state 1 and state 3 is, for example, 10 / (Vin−Vcf), and the conduction ratio of the second switching element 52 is, for example, 10 / Vin. And it is sufficient. The flow ratio of the first and

second switching elements

51 and 52 is an example, and may be set to an appropriate ratio according to conditions such as the input voltage difference of each DC voltage conversion unit 1.

The charge necessity determination unit 13 outputs a normal drive control command when the above-described expression (2) is satisfied, and the drive pulse generation unit 14 performs normal drive when the normal drive control command is input. The pulse generator 141 generates each drive pulse for normal drive control, outputs it to each of the first switching element 51 and the second switching element 52, and starts normal drive control.

Therefore, when the input voltage Vin> Vout (for example, the DC voltage converter 1b in FIG. 1), the charge / discharge capacitor 7 is charged by performing the charge drive control from the control stop state, and the charge / discharge capacitor 7 is charged. By performing normal drive control in the state that has been achieved, it is possible to shift to a steady state.

As described above, according to the DC / DC power converter of the embodiment, in each of the DC voltage converters connected in parallel, the charge / discharge capacitor is turned off by turning off the first and

second switching elements

51 and 52. 7 is connected in series to the charging auxiliary capacitor 10 that is charged together with the charging / discharging capacitor 7 by the energy stored in the reactor 4, and the backflow preventing diode 8 that prevents the reverse flow of the charge stored in the charging auxiliary capacitor 10; A Zener diode 9 connected in reverse series to the backflow prevention diode 8 and maintaining the voltage value of the auxiliary charging capacitor 10 within a certain range with respect to the connection point of the first and second

output smoothing capacitors

11 and 12; And a normal drive control for converting the input voltage into a desired output voltage, and the voltage across the charge / discharge capacitor 10 is predetermined. When the pressure is less than the pressure, the first switching element 51 is turned on after the second switching element 52 or both the first switching element 51 and the second switching element 52 are turned on to accumulate energy in the reactor 4. And the second switching element 52 is turned off, and the charge drive control having the switching pattern for transferring the energy stored in the reactor 4 to the charge / discharge capacitor 7 and the charge auxiliary capacitor 10 is performed. Even when a plurality of DC power supplies having different output voltages are connected to the converter, the output voltage of each DC power supply can be boosted to a desired DC voltage.

In the above-described embodiment, the example in which the charge drive control is performed before the transition from the control stop state to the steady state, that is, before the normal drive control is started, has been described. It is also possible to perform charge drive control. That is, when it is determined that the charging / discharging capacitor is insufficiently charged during the normal driving control, the charging / discharging capacitor can be charged by shifting to the charging driving control.

In the embodiment described above, when the charge drive control is performed, two switching patterns are provided, and whether the voltage difference between the input voltage Vin and the voltage Vcf across the charge / discharge capacitor is greater than 100V or less than 100V. However, the potential difference between the input voltage Vin and the voltage Vcf across the charge / discharge capacitor when switching the switching pattern is set according to the conditions of the system to which the DC / DC power converter is applied. do it. Or depending on conditions, it is also possible to operate with only one of the two switching patterns.

Also, the DC / DC power conversion device according to the embodiment is suitable for use in a solar power generation system including a plurality of solar cell module groups. Since the number of solar cell modules in series varies depending on, for example, the condition of the roof on which the solar cell module group is installed, the output voltage differs for each solar cell module group. Since the DC / DC power converter according to the embodiment operates independently for each DC voltage converter, an optimum boosting operation can be performed for each solar cell module group.

In addition, a general switching element is formed of a silicon (silicon: Si) -based semiconductor, and the first and second switching elements of each DC voltage conversion unit of the DC / DC power conversion device described in the embodiment. As for, it is preferable that it is formed of a wide band gap (WBG) semiconductor having a large energy bandwidth compared to a Si-based semiconductor. Examples of the WBG semiconductor include silicon carbide (SiC), gallium nitride (GaN) -based materials, and diamond.

In the DC voltage converter where the difference between the input voltage and the boosted output voltage is large, the switching operation frequency of the first and second switching elements increases, and the switching loss and conduction loss also increase. The amount of heat generated by the element also increases. Therefore, in the design stage, a maximum heat generation condition in a system or the like to which the DC / DC power converter is applied, that is, a condition that causes the highest switching operation frequency is assumed in advance, and the limit temperature of the switching element is not exceeded under the condition. Thus, the size of the heat sink connected to the switching element is determined.

In addition, in the DC voltage converter where the difference between the input voltage and the boosted output voltage is small, the switching operation frequency of the first and second switching elements is reduced, and the switching loss and conduction loss are also reduced. The amount of heat generated by each switching element is also reduced. For this reason, the size of the heat sink designed assuming the above-mentioned maximum heat generation condition has a large tolerance for the limit temperature of the switching element, and a large installation space is required, and the DC / DC power converter is enlarged. To do. In addition, the cost of the heat sink and the cost of the DC / DC power converter increase.

On the other hand, the WBG semiconductor has lower switching loss and conduction loss than the Si-based semiconductor, has high heat resistance, and can operate at a high temperature. Therefore, the size of the heat sink can be reduced by using the switching element formed of the WBG semiconductor as compared with the case of using the switching element formed of the Si-based semiconductor.

Furthermore, since the switching element formed of such a WBG semiconductor has high voltage resistance and high allowable current density, the switching element itself can be downsized.

Therefore, by using switching elements formed of WBG semiconductors as the first and second switching elements, the DC / DC power converter can be reduced in size and cost even when the above-described maximum heat generation condition is assumed. Can be planned.

Furthermore, for example, even when assuming a case where a large difference occurs in the switching operation frequency of each DC voltage conversion unit to which each solar cell module group is connected, the first and second switching elements of each DC voltage conversion unit are cooled. The heat sink can be configured with an optimal size that does not provide an excess margin, and by extension, this DC / DC power conversion device can be applied to support various constraints such as roofs or houses. A power generation system can be constructed.

The configurations described in the above embodiments are examples of the configurations of the present invention, and can be combined with other known techniques, and a part of the configurations is omitted without departing from the gist of the present invention. Needless to say, it is possible to change the configuration.

1, 1a, 1b DC

voltage conversion unit

2, 2a, 2b

DC power supply

3, 3a, 3b Input

side smoothing capacitor

4, 4a,

4b Reactor

7, 7a, 7b Charge /

discharge capacitor

8, 8a, 8b

Backflow prevention diode

9, 9a ,

9b Zener diode

10, 10a, 10b Charging auxiliary capacitor 11 First output-side smoothing capacitor 12 Second output-

side smoothing capacitor

13, 13a, 13b Charging

necessity determination unit

14, 14a, 14b Drive

pulse generation unit

51, 51a , 51b

First switching element

52, 52a, 52b

Second switching element

61, 61a,

61b First diode

62, 62a,

62b Second diode

100, 100a,

100b Drive controller

141, 141a, 141b Normal

drive Pulse generator

142, 142a, 142b Charging drive Pulse generator

Claims

A reactor connected to a DC power source, a plurality of switching elements connected in series for switching the output of the reactor, a charge / discharge capacitor charged / discharged by switching of the plurality of switching elements, a charge path and a discharge path of the charge / discharge capacitor A plurality of diodes, and a plurality of DC voltage converters including a drive control unit that drives and controls the plurality of switching elements,
A plurality of output smoothing capacitors connected in series to smooth parallel outputs of the plurality of DC voltage converters;
With
The DC voltage converter is
A charge auxiliary capacitor that is connected in series with the charge / discharge capacitor by turning off the plurality of switching elements, and that is charged together with the charge / discharge capacitor by the energy stored in the reactor,
A backflow prevention diode for preventing a backflow of charges stored in the charging auxiliary capacitor;
A Zener diode connected in anti-series with respect to the backflow prevention diode, and maintaining a voltage value of a charging auxiliary capacitor within a certain range with respect to a connection point of the plurality of smoothing capacitors for output;
With
The drive control unit performs normal drive control for converting an input voltage into a desired output voltage, and performs charge drive control for charging the charge / discharge capacitor when a voltage across the charge / discharge capacitor is less than a predetermined voltage. DC / DC power converter characterized by performing.
The DC / DC power converter according to claim 1, wherein the drive control unit performs the charge drive control before the start of the normal drive control.
The DC / DC power converter according to claim 1, wherein the drive control unit performs the charge drive control after the start of the normal drive control.
The DC / DC power converter according to claim 1, wherein the switching element is formed of a wide band gap semiconductor.
The DC / DC power converter according to claim 4, wherein the wide band gap semiconductor is silicon carbide, a gallium nitride-based material, or diamond.
A plurality of solar cell module groups;
The DC / DC power converter according to claim 1, wherein each output voltage of the plurality of series of solar cell module groups is input to each of the DC voltage converters.
An inverter that converts a DC voltage supplied from the DC / DC power converter to an AC voltage;
A photovoltaic power generation system comprising:
The solar power generation system according to claim 6, wherein the switching element is formed of a wide band gap semiconductor.
The solar power generation system according to claim 7, wherein the wide band gap semiconductor is silicon carbide, a gallium nitride-based material, or diamond.