JP2012253967A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that allows reducing the operation loss of circuit elements and allows achieving high conversion efficiency.SOLUTION: In a DC-DC converter 10 that is provided with a filter circuit 14 having a smoothing reactor Lb and a smoothing capacitor Cb at a subsequent stage of a rectifier circuit 13 on a secondary side of an insulating transformer 12, a resonant capacitor Cx is connected in series between a secondary-side coil 12b of the insulating transformer 12 and the rectifier circuit 13. An inverter circuit 11 on a primary side is composed of a full-bridge circuit having switching elements SW1 to SW4, a switching operation is performed at a switching frequency in response to a resonant frequency of the smoothing reactor Lb of the filter circuit 14 and the resonant capacitor Cx.

Description

  The present invention relates to a power conversion device including a switching circuit and an insulating transformer.

  Conventionally, there has been a power converter that generates high-frequency AC power from DC power in a switching circuit such as an inverter circuit, converts the generated high-frequency AC power into a predetermined voltage with an insulation transformer, and converts it into DC power again and outputs it. Are known.

  For example, the power conversion device (switching power supply circuit) disclosed in Patent Document 1 is configured by using a chopper circuit as a switching circuit, and similarly converts DC power into high-frequency AC power in the switching operation of the circuit. Then, it is converted into a predetermined voltage through an insulating transformer, converted into direct current again by a rectifier circuit, and output.

JP 2007-104804 A

  By the way, in the rectifier circuit on the secondary side of the insulation transformer, if an operation loss occurs due to the rectification operation of the rectifier elements such as diodes and switching elements constituting the circuit, the high efficiency of the apparatus is hindered.

  In the apparatus disclosed in Patent Document 1, a series resonance capacitor is provided between the secondary coil of the insulating transformer and the rectifier circuit, and the resonance operation is performed by the leakage inductance of the secondary coil and the series resonance capacitor. ing. Thus, switching with zero current and zero voltage (ZCS, ZVS), so-called soft switching, is performed during the rectifying operation of the rectifying element, and operation loss in the rectifying element is reduced. Incidentally, in the apparatus disclosed in Patent Document 1, the leakage inductance of the primary side coil is also used.

  However, the configuration using the leakage inductance of the insulating transformer means loose coupling of the transformer, which means that the power transmission efficiency of the transformer is low. Therefore, it is not suitable for a power conversion device using a high-efficiency power transmission efficiency for an insulating transformer, for example, a device for high-power applications because the leakage inductance of the transformer cannot be used, and power conversion using a high-efficiency transformer Application to devices is desired.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a power conversion device that can reduce the operation loss of circuit elements and increase the conversion efficiency. is there.

  In order to solve the above-mentioned problem, the invention described in claim 1 is composed of a full bridge circuit using a switching element, converts input DC power into high-frequency AC power by switching operation, An inverter circuit to be supplied to the side coil, an insulating transformer that converts the high-frequency AC power supplied to the primary coil to a secondary coil and converts the voltage to the secondary coil, and a high-frequency AC output from the secondary coil of the insulating transformer A power conversion device including a rectifier circuit that rectifies power to convert to direct current, and includes a filter circuit having a smoothing reactor and a smoothing capacitor at a subsequent stage of the rectifying circuit, and resonant with the smoothing reactor The resonant capacitor to be operated is connected in series between the secondary coil of the isolation transformer and the rectifier circuit, and the resonant frequency is Flip was that it has to perform a switching operation at a switching frequency of said inverter circuit and the gist thereof.

  According to the present invention, in a power conversion device in which a filter circuit having a smoothing reactor and a smoothing capacitor is provided in a subsequent stage of a rectifying circuit on the secondary side of an insulating transformer, a resonant capacitor is provided between the secondary coil of the insulating transformer and the rectifying circuit. Are connected in series. Then, the switching operation is performed on the inverter circuit on the primary side of the transformer at a switching frequency corresponding to the resonance frequency of the smoothing reactor of the filter circuit and the resonance capacitor. As a result, the impedance on the secondary side of the isolation transformer is reduced, that is, the phase shift of the current with respect to the voltage is reduced, so that the operating loss for the rectification operation in the elements constituting the secondary rectifier circuit is reduced. . Further, since the primary side of the insulation transformer is also affected by the secondary side, the operation loss in the elements constituting the primary side inverter circuit is also reduced.

  The gist of the invention according to claim 2 is that, in the power conversion device according to claim 1, the inverter circuit has a capacitor connected in parallel with each switching element constituting the circuit.

  In the present invention, since a capacitor is connected in parallel with each switching element constituting the inverter circuit, a switching operation (ZVS) at zero voltage is possible, and an operation loss in the switching element is reduced.

The gist of the invention described in claim 3 is that, in the power conversion device according to claim 1 or 2, the rectifier circuit is configured by a full bridge circuit using a diode.
According to the present invention, in a rectifier circuit constituted by a full bridge circuit of diodes, operation loss (conduction loss, recovery loss) in each diode is reduced.

  The invention described in claim 4 is the power converter according to claim 1 or 2, wherein the rectifier circuit is configured by a synchronous rectifier circuit including a full bridge circuit using a switching element. And

According to the present invention, in a synchronous rectifier circuit including a full bridge circuit of switching elements, loss during switching operation of each switching element is reduced.
The gist of the invention according to claim 5 is that, in the power conversion device according to claim 4, the rectifier circuit has a capacitor connected in parallel with each switching element constituting the circuit.

  In the present invention, since a capacitor is connected in parallel with each switching element constituting the rectifier circuit, a switching operation (ZVS) at zero voltage is possible, and an operation loss in the switching element is reduced.

  The invention according to claim 6 is the power converter according to claim 4 or 5, further comprising a smoothing capacitor for smoothing the input DC power, and a reactor is connected in series between the smoothing capacitor and the inverter circuit. The gist is that they are connected.

  In the present invention, a reactor is connected in series between the smoothing capacitor that smoothes the input DC power and the inverter circuit. Here, since the rectifier circuit on the secondary side of the isolation transformer is a synchronous rectifier circuit, the circuit can be operated as an inverter circuit, while the inverter circuit on the primary side of the transformer can be operated as a synchronous rectifier circuit. is there. In this case, the reactor added to the input side also functions as a filter circuit with the smoothing capacitor on the input side, and becomes an output through the same filter circuit in the reverse direction as well as the forward direction. In other words, the bidirectional power conversion device can be used by appropriately switching the input and output.

  The gist of the invention according to claim 7 is that, in the power converter according to claim 1 or 2, the rectifier circuit is configured by a voltage doubler rectifier circuit using a diode and a capacitor.

According to the present invention, in a voltage doubler rectifier circuit using a diode and a capacitor, operation loss (conduction loss, recovery loss) in each diode is reduced.
The invention according to claim 8 is the power conversion device according to any one of claims 1 to 7, wherein the switching frequency of the inverter circuit is such that the resonant capacitor and the smoothing reactor on the secondary side of the insulating transformer The gist of this is that it is set to match the resonance frequency.

  In the present invention, the switching frequency of the inverter circuit is set so as to coincide with the resonant frequency of the secondary side resonant capacitor and the smoothing reactor of the insulating transformer. Thereby, since the impedance on the secondary side of the insulation transformer is minimized, the operation loss for the rectification operation in the elements constituting the secondary side rectifier circuit is further reduced. Further, since the primary side of the isolation transformer is also affected by the secondary side, it is possible to expect a further reduction in operation loss in the elements constituting the primary side inverter circuit.

  ADVANTAGE OF THE INVENTION According to this invention, the operating loss of a circuit element can be reduced and the power converter device with which conversion efficiency is made high can be provided.

The circuit diagram of the DC-DC converter as a power converter device in an embodiment. The wave form diagram for demonstrating operation | movement of a converter. The wave form diagram for demonstrating operation | movement of a converter. The wave form diagram for demonstrating operation | movement of a converter. The wave form diagram for demonstrating operation | movement of a converter. The wave form diagram for demonstrating operation | movement of a converter. The circuit diagram of the converter in another example. The circuit diagram of the converter in another example. The circuit diagram of the converter in another example.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
The DC-DC converter 10 of this embodiment shown in FIG. 1 inputs DC power output from a DC power source such as a solar power generation apparatus, and outputs the input DC power as output DC power converted into a predetermined voltage. It is. Incidentally, as the DC power source, there are a fuel cell power generation device, a storage battery device, a commercial AC power DC conversion device, and the like in addition to a solar power generation device.

The DC-DC converter 10 includes a smoothing capacitor Ca, an inverter circuit 11, an insulating transformer 12, a resonant capacitor Cx, a rectifier circuit 13, and a filter circuit 14.
On the primary side of the insulation transformer 12, an inverter circuit 11 is provided as a switching circuit. The inverter circuit 11 is configured by a full bridge (H bridge) circuit using four switching elements SW1 to SW4 such as IGBTs. Further, reverse switching diodes D1 to D4 and capacitors C1 to C4 are connected in parallel to the switching elements SW1 to SW4, respectively. The inverter circuit 11 converts the DC power input through the smoothing capacitor Ca into high-frequency AC power by turning on / off the switching elements SW1 to SW4 based on the control of the control circuit 15, and converts the converted high-frequency AC power. The insulation transformer 12 is supplied to the primary coil 12a.

  The insulating transformer 12 converts the high-frequency AC power supplied to the primary side coil 12a into a predetermined voltage by the secondary side coil 12b. As the insulating transformer 12 used in the present embodiment, a transformer with high coupling and high power transmission efficiency is used, and the DC-DC converter 10 of the present embodiment is suitable for high power applications. Accordingly, almost no leakage inductance is generated on the primary side and the secondary side of the insulating transformer 12. As a high power application, a full bridge circuit including four switching elements SW1 to SW4 is used for the inverter circuit 11 described above.

  On the secondary side of the insulation transformer 12, a resonance capacitor Cx is connected in series to the secondary coil 12b, and a rectifier circuit 13 is provided at the subsequent stage. The rectifier circuit 13 is configured by a full bridge circuit using four diodes D5 to D8. A filter circuit 14 is provided following the rectifier circuit 13. The filter circuit 14 includes a smoothing reactor Lb and a smoothing capacitor Cb. The filter circuit 14 smoothes the DC power that has passed through the rectifier circuit 13 using the smoothing reactor Lb and the smoothing capacitor Cb, and outputs the output DC power to the load side. In addition, although it is a comparatively large component, the reactor Lb is used for the filter circuit 14 for a high power use.

In the present embodiment, the smoothing reactor Lb functioning as the filter circuit 14 is caused to resonate with the previous resonance capacitor Cx.
Here, when the secondary side of the insulating transformer 12 is considered as a simple equivalent circuit, it can be considered as a circuit in which the secondary side coil 12b, the resonant capacitor Cx, the smoothing reactor Lb, and a load are connected in series. In such an equivalent circuit, the impedance is reduced by bringing the frequency of the high-frequency AC power generated in the secondary coil 12b close to the resonance frequency of the resonance capacitor Cx and the smoothing reactor Lb. The frequency of the high-frequency AC power generated in the secondary coil 12b is the switching frequency of the inverter circuit 11 (switching elements SW1 to SW4), and the impedance of the equivalent circuit is reduced by bringing this switching frequency closer to the resonance frequency. When the switching frequency is matched to the resonance frequency, the impedance of the equivalent circuit is minimized.

  Therefore, in the control circuit 15 that controls the switching operation of the inverter circuit 11 (switching elements SW1 to SW4), the switching frequency is set in consideration of the resonance frequencies of the resonance capacitor Cx and the smoothing reactor Lb, and is matched in this embodiment. Is set to In the PWM control of the inverter circuit 11 by the control circuit 15, appropriate output power is converted from the input power at that time and output.

Next, the operation (action) of the DC-DC converter 10 of the present embodiment will be described.
FIG. 2 is a waveform diagram showing an operation mode of the DC-DC converter 10, and a control signal (see the switch gate voltage in the figure) is input from the control circuit 15 to the gates of the switching elements SW 1 to SW 4 of the inverter circuit 11. The switching elements SW1 to SW4 are alternately switched in a predetermined combination to generate high-frequency AC power, which is supplied to the subsequent isolation transformer 12.

  At this time, since the switching frequency of the inverter circuit 11 is matched with the resonance frequency of the secondary side resonance capacitor Cx and the smoothing reactor Lb of the insulating transformer 12, the impedance of the secondary side equivalent circuit is minimized. This is because the phase shift of the current with respect to the voltage is improved and a sine wave current having a specific frequency (resonance frequency) is obtained, so that the diodes D5 to D8 of the rectifier circuit 13 are turned off after the conduction current becomes substantially zero. The voltage becomes substantially zero and turns on. That is, the diodes D5 to D8 of the rectifier circuit 13 can perform the switching operation (ZCS, ZVS) at zero current and zero voltage (see the rectifier diode conduction current and applied voltage in the figure), and the operation loss (conduction) during the rectification operation. Loss, recovery loss) and the noise associated therewith are reduced.

  In addition, in the inverter circuit 11 on the primary side of the insulating transformer 12, a sinusoidal current flows similarly under the influence of the secondary side of the transformer 12 (see the transformer applied current in the figure). Thereby, switching (ZCS) by substantially zero current of each switching element SW1-SW4 of the inverter circuit 11 is attained (refer switch electrical current in the figure). In addition, the capacitors C1 to C4 connected in parallel to the switching elements SW1 to SW4 enable the switching elements SW1 to SW4 to be switched at substantially zero voltage (ZVS) (see the switch application voltage in the figure). Further, the diodes D1 to D4 connected in parallel to the switching elements SW1 to SW4 can also perform zero current and zero voltage switching (ZCS, ZVS) as in the secondary side. Thus, even on the primary side of the insulating transformer 12, the operating loss and noise of the switching elements SW1 to SW4 and the diodes D1 to D4 are reduced.

  Incidentally, in the simulation shown in FIG. 2 described above, the input voltage is 380 V, for example, and the output power is 5500 W. In addition, in the simulation shown in FIG. 3, the input voltage is, for example, 380 V and the output power is 3000 W, and in the simulation shown in FIG. 4, the input voltage is, for example, 380 V and the output power is 500 W. In the simulation shown in FIG. 5, the input voltage is 450 V and the output power is 3000 W, for example, and in the simulation shown in FIG. 6, the input voltage is 450 V and the output power is 500 W, for example. Assuming a photovoltaic power generation device as a DC power source on the input side, the input power is greatly changed.

  3 and FIG. 4 is an aspect in which the duty of the control signal for controlling the inverter circuit 11 is set to the maximum as in FIG. In these embodiments, the diodes D5 to D8 of the secondary side rectifier circuit 13 are ZCS and ZVS, the switching elements SW1 to SW4 of the primary side inverter circuit 11 are ZCS and ZVS, and the diodes D1 to D4 are ZCS and ZVS. Operation is to be performed.

  5 and 6 is an aspect in which the duty of the control signal for controlling the inverter circuit 11 is set to be small. Even in these aspects, the diodes D5 to D8 of the secondary side rectifier circuit 13, the switching elements SW1 to SW4 of the primary side inverter circuit 11, and the diodes D1 to D4 each include a state in which some operating loss may occur. The operation at substantially ZCS and ZVS is possible.

Next, characteristic effects of the present embodiment will be described.
(1) In the DC-DC converter 10 of the present embodiment in which the filter circuit 14 having the smoothing reactor Lb and the smoothing capacitor Cb is provided in the subsequent stage of the rectifier circuit 13 on the secondary side of the insulating transformer 12, the secondary of the insulating transformer 12 A resonant capacitor Cx is connected in series between the side coil 12 b and the rectifier circuit 13. Then, the switching operation is performed on the inverter circuit 11 on the primary side of the transformer 12 at a switching frequency corresponding to the resonance frequency of the smoothing reactor Lb of the filter circuit 14 and the resonance capacitor Cx. That is, since the impedance on the secondary side of the insulating transformer 12 is reduced, that is, the phase shift of the current with respect to the voltage is reduced, the operating loss for the rectifying operation in the diodes D5 to D8 constituting the secondary rectifier circuit 13 is reduced. (Conduction loss, recovery loss) can be reduced. In particular, in this embodiment, since the switching operation is performed at the switching frequency that matches the resonance frequency, the impedance on the secondary side of the transformer 12 is minimized, and further reduction of the loss in the diodes D5 to D8 can be expected. In addition, a noise reduction effect can be expected from a reduction in operation loss. Further, since the primary side of the insulating transformer 12 is also influenced by the secondary side, the operation loss in the switching elements SW1 to SW4 constituting the primary side inverter circuit 11 can be reduced. From these, the conversion efficiency in the DC-DC converter 10 can be further increased.

  (2) Since the capacitors C1 to C4 are connected in parallel with the switching elements SW1 to SW4 constituting the inverter circuit 11, a switching operation (ZVS) at zero voltage can be performed by this, so that the switching element SW1 The operation loss in .about.SW4 can be more reliably reduced. Thereby, it can contribute to the improvement of the conversion efficiency of the DC-DC converter 10.

In addition, you may change embodiment of this invention as follows.
In the above embodiment, the switching frequency of the inverter circuit 11 is matched with the resonant frequency of the resonant capacitor Cx and the smoothing reactor Lb, but the secondary side impedance is sufficiently small, and the operating loss in the elements constituting the rectifier circuit 13 As long as the frequency can be sufficiently reduced, the switching frequency may be set slightly shifted in the vicinity of the resonance frequency.

  In the above embodiment, the diodes D1 to D4 and the capacitors C1 to C4 are connected in parallel to the switching elements SW1 to SW4 of the inverter circuit 11, respectively, but the configuration of the inverter circuit 11 is appropriately changed, such as omitting the capacitors C1 to C4. May be.

In the above embodiment, the rectifier circuit 13 on the secondary side of the transformer 12 is configured by a bridge circuit of diodes D5 to D8, but the circuit configuration is not limited to this.
For example, as shown in FIG. 7, a synchronous rectifier circuit 13 </ b> A composed of a full bridge circuit of switching elements SW <b> 5 to SW <b> 8 may be used. Diodes D5 to D8 and capacitors C5 to C8 are connected in parallel to the switching elements SW5 to SW8, respectively. Also in the synchronous rectifier circuit 13A, the operation loss in the switching elements SW5 to SW8 during the switching operation is reduced. Further, since the switching operation (ZVS) at zero voltage is also possible by the capacitors C5 to C8 connected in parallel with the switching elements SW5 to SW8, the operation loss in the switching elements SW5 to SW8 can be more reliably reduced.

  In the mode shown in FIG. 8, in addition to the mode shown in FIG. 7, a reactor La may be connected in series between the input-side smoothing capacitor Ca and the inverter circuit 11. Here, since the rectifier circuit 13A on the secondary side of the isolation transformer 12 is a synchronous rectifier circuit, the circuit 13A is operated as the inverter circuit 11, while the inverter circuit 11 on the primary side of the transformer 12 is used as the synchronous rectifier circuit. It is possible to operate. In this case, the reactor La added on the input side also functions as a filter circuit with the smoothing capacitor Ca on the input side, and becomes an output through the same filter circuit in the reverse direction as in the forward direction. That is, it is a bidirectional power conversion device that can be used by appropriately switching input and output.

  Incidentally, such a bidirectional power conversion device is suitable when a storage battery device requiring bidirectional power transfer is used, for example, to extract or charge power as a DC power source on the input side.

  Further, as shown in FIG. 9, a voltage doubler rectifier circuit 13B using diodes D9 and D10 and capacitors C9 and C10 may be used. That is, the diode D9 is connected in the forward direction and the diode D10 is connected in parallel to the resonant capacitor Cx, and the capacitors C9 and C10 are connected between the cathode of the diode D9 and the anode of the diode D10. The capacitors C9 and C10 are connected to the other end of the secondary coil 12b. The cathode of the diode D9 and the anode of the diode D10 are connected to the subsequent filter circuit 14. Also in such a voltage doubler rectifier circuit, the operation loss (conduction loss, recovery loss) concerning the rectification operation in each of the diodes D9 and D10 is reduced.

  Further, a rectifier circuit other than the rectifier circuit 13 (diode bridge circuit), the synchronous rectifier circuit 13A, and the voltage doubler rectifier circuit 13B may be used.

DESCRIPTION OF SYMBOLS 11 Inverter circuit 12 Insulation transformer 12a Primary side coil 12b Secondary side coil 13 Rectifier circuit 13A Synchronous rectifier circuit (rectifier circuit)
13B Voltage doubler rectifier circuit (rectifier circuit)
14 Filter circuit SW1-SW4 Switching element SW5-SW8 Switching element La Reactor Lb Smoothing reactor Ca Smoothing capacitor Cb Smoothing capacitor Cx Resonance capacitor C1-C4 Capacitor C5-C8 Capacitor C9, C10 Capacitor D5-D8 Diode D9, D10 Diode

Claims (8)

An inverter circuit that is configured by a full bridge circuit using a switching element, converts input DC power to high-frequency AC power by a switching operation, and supplies the high-frequency AC power to a primary coil of a subsequent isolation transformer;
An insulating transformer that converts high-frequency AC power supplied to the primary coil to a secondary coil by converting the voltage;
A power converter comprising: a rectifier circuit that rectifies high-frequency AC power output from a secondary coil of the insulation transformer and converts the high-frequency AC power into a direct current;
The latter stage of the rectifier circuit is provided with a filter circuit having a smoothing reactor and a smoothing capacitor,
A resonance capacitor that resonates with the smoothing reactor is connected in series between the secondary coil of the isolation transformer and the rectifier circuit, and the switching operation is performed at the switching frequency of the inverter circuit according to the resonance frequency. The power converter characterized by having made it. The power conversion device according to claim 1,
In the inverter circuit, a capacitor is connected in parallel with each switching element constituting the circuit. The power conversion device according to claim 1 or 2,
The rectifier circuit is configured by a full bridge circuit using a diode. The power conversion device according to claim 1 or 2,
The rectifier circuit is configured by a synchronous rectifier circuit including a full bridge circuit using a switching element. The power conversion device according to claim 4,
The rectifier circuit includes a capacitor connected in parallel with each switching element constituting the circuit. The power conversion device according to claim 4 or 5,
A power converter comprising a smoothing capacitor for smoothing the input DC power, and a reactor connected in series between the smoothing capacitor and the inverter circuit. The power conversion device according to claim 1 or 2,
The rectifier circuit is configured by a voltage doubler rectifier circuit using a diode and a capacitor. In the power converter device of any one of Claims 1-7,
The switching frequency of the inverter circuit is set to coincide with the resonance frequency of the resonant capacitor and the smoothing reactor on the secondary side of the insulating transformer.

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