JP2006304381A - Power conversion equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide power conversion equipment which achieves the downsizing of a high-frequency transformer even to a high step-up ratio without increasing the number of pieces of secondary windings of a high-frequency transformer, and the loss reduction of a semiconductor element such as a switching element and a diode. <P>SOLUTION: The loss reduction of switching elements Q1-Q4 is achieved together with the downsizing of the high-frequency transformer 13 by arranging a voltage doubler rectifier means 15 on the secondary side of the high-frequency transformer 13 and letting a resonance current flow thereby achieving the reduction of the pieces of the secondary windings and lower withstand voltages of parts. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power conversion device that converts DC power, such as a solar cell or a fuel cell, into AC power having a commercial frequency and injects power into the system.

  Conventionally, as this type of power conversion device, for example, a resonance capacitor and a switching element are arranged on the primary side of a high-frequency transformer, and a zero voltage switching operation is performed by resonating the voltage waveform of the switching element. By performing sinusoidal modulation with a double period, and further rectifying high-frequency components with a diode and a capacitor on the secondary side of the high-frequency transformer, and switching the polarity with a secondary inverter arranged on the secondary side of the high-frequency transformer, There has been a high-efficiency power converter that generates a sine wave current with a rate of 1 (see, for example, Patent Document 1).

  A power converter used in the past will be described with reference to FIGS.

  In FIG. 3, the 1st inverter 1 converts the electric power of the direct-current power supply 2 into a high frequency electric power. This is realized by the switching element 3 of the first inverter 1 being repeatedly turned on and off.

  Normally, when the switching element 3 is turned off, the current flowing between the collector and the emitter is cut off. Therefore, the excitation energy accumulated in the high-frequency transformer 4 is charged / discharged with the resonance capacitor 5, thereby The collector-emitter voltage has a resonance waveform as shown in FIG.

  Next, zero voltage switching is realized by turning on the switching element 3 during a period in which the collector-emitter voltage becomes zero and a current flows through a diode connected in reverse parallel to the switching element 3.

6 is a rectifier, 7 is a second inverter, 8 is a smoothing capacitor, and 9 is a system.
JP 2000-32751 A

  However, in the conventional configuration, the output voltage of the high-frequency transformer is equal to or less than the value obtained by multiplying the input voltage by the winding ratio between the primary and secondary, but when a particularly high step-up ratio is required, the number of primary windings is Since there is a lower limit, it is necessary to increase the number of secondary windings of the high-frequency transformer in consideration of the operating frequency of the inverter. At the same time, the secondary side needs to have a breakdown voltage higher than the output voltage. There is a limit to weight reduction.

  The present invention solves the above-described conventional problems, and by arranging the voltage doubler rectifying means on the secondary side of the high-frequency transformer, the step-up ratio of the high-frequency transformer can be reduced, so that the number of secondary windings is reduced. It is an object of the present invention to provide a power conversion device capable of reducing the size of a high-frequency transformer by reducing the structural breakdown voltage.

   In order to achieve the above object, a power converter according to the present invention has a voltage doubler rectifier connected to the secondary side of a high-frequency transformer to supply rectified high-frequency power to a second inverter. It is what.

  The power conversion device according to the present invention connects the voltage doubler rectifier to the secondary side of the high-frequency transformer and reduces the primary / secondary turns ratio of the high-frequency transformer substantially by half compared to the case of the rectifier bridge. By reducing the number of windings, it is possible to reduce the size of the high-frequency transformer and to provide a power conversion device that expands the degree of design freedom of the number of high-frequency transformer primary and secondary windings under input / output voltage conditions with a large step-up ratio.

  The first invention is a full bridge configuration comprising two or more voltage dividing capacitors for dividing a DC voltage, a high-frequency transformer having an intermediate terminal on the primary side, and two arms in which two switching elements are connected in series. The first inverter, the first to fourth resonant capacitors of each switching element, and the second inverter for controlling the output current, and the resonant voltage between the intermediate voltage by the voltage dividing capacitor and the intermediate terminal of the high-frequency transformer. In the configuration in which the switching element performs zero voltage switching operation regardless of the operation of each arm, the current limiting reactor and the voltage doubler rectifying means are connected between the secondary side of the high frequency transformer and the second inverter, It is possible to realize a power conversion device that can reduce the number of secondary turns and reduce the size of the high-frequency transformer.

  In particular, according to the second invention, in the first invention, the voltage doubler rectifier means is a half-wave rectifier comprising a smoothing capacitor and a diode, whereby a simple and inexpensive power converter can be realized.

  According to a third invention, in any one of the first and second inventions, the resonant frequency of the resonant capacitor and the current limiting reactor constituting the rectifying means is set to be equal to or lower than the operating frequency of the first inverter, whereby the first diode This makes it possible to realize a low-loss power converter.

  In particular, the fourth invention is one in which the power converter of the first to third inventions is mounted on a solar cell.

  In the fifth aspect of the invention, in particular, the power conversion device of the first to third aspects of the invention is mounted on a fuel cell.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment.

(Embodiment 1)
In FIG. 1, a switching element Q1 and a switching element Q2 connected in series, a switching element Q3 and a switching element Q4 constitute a first inverter 11, and between the collector-emitter (or drain-source) of each switching element Q1 to Q4. Are connected to resonance capacitors 12a to 12d for zero voltage switching.

  The output of the first inverter 11 is connected to the primary side of the high-frequency transformer 13, and the current-limiting reactor 14, the voltage doubler rectifying means 15, and the second inverter 16 are connected to the secondary side of the high-frequency transformer 13. And connected to the system 17.

  The voltage of the DC power source is divided by two voltage dividing capacitors 18, and an intermediate voltage terminal is connected to an intermediate terminal on the primary side of the high-frequency transformer 13 via a resonant reactor 19. The voltage doubler rectifying means 15 is composed of a diode 20 and a smoothing capacitor 21.

  About the power converter device comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  Switching element Q1 and switching element Q4, switching element Q2 and switching element Q3 have high-frequency switching with a phase of 180 degrees, respectively, so that when the negative side of the DC input power source is zero, the primary of high-frequency transformer 13 The side (a) point voltage is a high-frequency voltage having an amplitude of zero and the DC voltage Vin.

  Here, when the switching elements (for example, Q1 and Q4) that have been turned on are turned off, the resonant capacitors 15a and 15d connected in parallel to the respective switching elements are charged, and the switching elements (in this case, Q2) that have been disabled are charged. , Q3) and the parallel resonant capacitors 15b, 15c are discharged, and the current is regenerated to the DC input power source when the reverse conducting diode becomes conductive.

  Zero voltage switching is performed by turning on the switching elements Q2 and Q3 at the timing when the reverse conducting diode is conducting. When the switching element Q2 and the switching element Q3 are conductive, the high-frequency voltage output to the secondary side of the high-frequency transformer 13 is limited in current by the current-limiting reactor 14, and the diode 20 constituting the voltage doubler rectifier 15 is conductive. When the smoothing capacitor 21 is charged and the switching element Q1 and the switching element Q4 are turned on, a reverse voltage is applied to the diode 20, so that the sum of the voltage and the voltage of the high-frequency transformer 13 is supplied to the second inverter 16. Applied.

  At this time, due to the action of the current limiting reactor 14, the input current to the second inverter 16 becomes a resonance waveform whose frequency is determined by the current limiting reactor 14 and the smoothing capacitor 21, and the diode 19 associated with the switching of the first inverter 11 Reduces recovery loss.

  Further, by selecting the capacity of the smoothing capacitor 121 that changes the voltage according to the output current during the conduction of the first inverter 11, it flows between the collector and emitter (or drain and source) of the switching elements constituting the first inverter 11. Using the current as a resonance waveform, the current at turn-off is reduced to reduce the switching loss.

  As described above, in the present embodiment, the voltage doubler rectifier is connected to the secondary side of the high-frequency transformer, and is configured with a smoothing capacitor and a diode having a small capacity, so that the number of secondary windings of the high-frequency transformer can be reduced. By greatly reducing the loss associated with switching of switching elements and diodes, it is possible to achieve downsizing and higher efficiency of the device.

(Embodiment 2)
FIG. 2 shows the operation of each part of the power conversion device according to the second embodiment of the present invention. The components are the same as those in the first embodiment, and the description is the same as in the first embodiment. Incorporate.

  In FIG. 2, the resonance frequency of the smoothing capacitor 21 constituting the current limiting reactor 14 and the voltage doubler rectifier 15 connected to the secondary side of the high frequency transformer 13 is selected to be equal to or lower than the operating frequency of the first inverter 11.

  When the switching elements Q1 and Q4 and the switching elements Q2 and Q3 constituting the inverter 11 perform high-frequency switching with a phase of 180 degrees, zero voltage switching is maintained.

  Here, when the output power is small or the input voltage is high, the first inverter 11 needs to increase the operating frequency, so that the power transmitted to the secondary side of the high-frequency transformer 13 also has a high frequency. Since the resonance frequency of the current limiting reactor 14 and the smoothing capacitor 21 is equal to or lower than the operating frequency of the first inverter 11, the current waveform of the switching element constituting the first inverter 11 and the input current waveform to the second inverter 16 are current limiting. Large vibrations at the resonance frequency of the reactor 14 and the smoothing capacitor 21 are avoided.

  As a result, when the switching element of the first inverter 11 is turned off, the current waveform including the diode 20 does not take a local maximum value, and an increase in loss at a specific operating frequency does not occur.

  As described above, in the present embodiment, by setting the resonance frequency of the resonance capacitor and the current-limiting reactor constituting the rectifying means to be equal to or lower than the operating frequency of the first inverter, the switching loss when the switching element is turned off, the rectification The recovery loss of the diode constituting the means can be reduced, and a highly efficient power conversion device can be realized.

  The power conversion device described above can be applied to a fuel cell, a solar cell, or the like so as to convert DC power into AC power having a commercial frequency.

  As described above, the power converter according to the present invention has the voltage doubler rectifier on the secondary side of the high-frequency transformer, and the power-converting ratio of the high-frequency transformer can be set for power conversion that requires a high step-up ratio or step-down ratio. Since it is possible to reduce the size of the device and increase the efficiency, it is possible to reduce the size of the device and increase the efficiency. It can also be applied to uses such as fuel cells and wind power generation.

Connection diagram of power conversion device according to embodiment 1 of the present invention Waveform diagram showing the operation of each part of the power converter according to Embodiment 2 of the present invention Connection diagram of conventional power converter Waveform diagram showing the operation of each part of a conventional power converter

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 1st inverter 12a-12d Resonance capacitor 13 High frequency transformer 14 Current limiting reactor 15 Voltage doubler rectifier 16 Second inverter 17 System 18 Voltage dividing capacitor 19 Resonant reactor 20 Diode 21 Smoothing capacitor

Claims (5)

Two or more voltage dividing capacitors for dividing a DC voltage; a high-frequency transformer having an intermediate terminal on the primary side; a first inverter having a full bridge configuration including two arms in which two switching elements are connected in series; The first to fourth resonant capacitors connected between the collector and the emitter of each switching element, a current-limiting reactor on the secondary side of the high-frequency transformer, a voltage doubler rectifier, and a second inverter for controlling the output current, A power converter that connects an intermediate voltage by a voltage dividing capacitor and an intermediate terminal of a high-frequency transformer with a resonance reactor. The power converter according to claim 1, wherein the voltage doubler rectifier rectifies high-frequency power with a smoothing capacitor and a diode. The power conversion device according to any one of claims 1 and 2, wherein a resonance frequency of the smoothing capacitor and the current limiting reactor is equal to or lower than an operating frequency of the first inverter. A fuel cell that converts direct-current power into alternating-current power at a commercial frequency by the power conversion device according to any one of claims 1 to 3. The solar cell which converted direct-current power into the alternating current power of commercial frequency with the power converter device of any one of Claims 1-3.

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