JP2015154525A - bidirectional flyback converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain downsizing by decreasing the number of switching elements.SOLUTION: When transmitting power from first input/output terminals 2p and 2n to second input/output terminals 3p and 3n, a control section 9 drives on a transistor Q1 during a period in which a voltage across the transistor Q1 becomes zero or negative in the state where transistors Q3 and Q4 are driven off, then drives off the transistor Q1 in the state where a transistor Q2 is driven on, and then maintains the state where the transistor Q2 is driven on, until at least the voltage across the transistor Q1 increases in a positive direction and then returns to zero. When transmitting power from the second input/output terminals 3p and 3n to the first input/output terminals 2p and 2n, the control section also similarly operates.

Description

  The present invention relates to an insulated resonant bidirectional flyback converter.

  Conventionally, a configuration using a full bridge circuit has been proposed for a bidirectional converter for high power. An insulated resonant bidirectional converter described in Patent Document 1 includes a low-voltage side switching unit having a single-phase full-bridge configuration, a high-voltage side switching unit having a single-phase full-bridge configuration, an insulating transformer that connects both switching units, and an insulating transformer And an LC resonance circuit connected between the one switching unit. A series circuit of an auxiliary resonant capacitor and an auxiliary switching element with an antiparallel diode is provided in parallel with the switching element of each arm of the switching unit.

  This bidirectional converter turns on the auxiliary switching element at the beginning of the ON period of the switching element in each arm of the low voltage side or high voltage side switching unit. As a result, the output voltage of the converter can be made higher than the transformer turns ratio, and robust characteristics can be obtained with respect to voltage fluctuations on the low voltage side and the high voltage side. Further, since the power consumption can be reduced by halving the voltage and current applied to one switching element, it is suitable for high power applications.

Japanese Patent No. 4527716

  However, the bidirectional converter described in Patent Document 1 requires four switching elements in each of the low voltage side switching unit and the high voltage side switching unit. This increases the circuit size and increases the cost.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a bidirectional flyback converter that is reduced in size by reducing the number of switching elements.

  The bidirectional flyback converter according to claim 1 includes a first converter unit provided on the first input / output terminal side, a second converter unit provided on the second input / output terminal side, a first converter unit and a second converter unit. A flyback transformer for connecting the converter unit and a control unit for controlling the first converter unit and the second converter unit are provided.

  The first converter unit includes a first switching element provided in series with one winding of the flyback transformer between the first input / output terminals, a first resonant capacitor provided in parallel with the first switching element, and a first A series circuit with two switching elements is provided. Similarly, the second converter unit includes a third switching element provided in series with the other winding of the flyback transformer between the second input / output terminals, and a second resonance provided in parallel with the third switching element. A series circuit of a capacitor and a fourth switching element is provided.

  When the control unit transmits power from the first input / output terminal to the second input / output terminal, a period in which the voltage across the first switching element is zero or negative while the third and fourth switching elements are driven off. The first switching element is turned on. At this time, since the first switching element performs zero voltage switching and zero current switching, switching loss can be reduced. When the first switching element is turned on, the current in one winding of the flyback transformer increases, and energy is accumulated in the flyback transformer.

  Thereafter, the control unit drives off the first switching element in a state where the second switching element is turned on. Thereby, a current flows through the other winding of the flyback transformer, and power is transmitted to the second input / output terminal side. The control unit maintains the second switching element in an ON state at least until the voltage across the first switching element increases in a positive direction and then returns to zero. As a result, a resonance current caused by the leakage inductance and the first resonance capacitor in one winding of the flyback transformer flows through the second switching element.

  The first resonant capacitor suppresses a sharp rise in voltage of the first switching element when the first switching element is turned off. Thereby, a 1st switching element becomes zero voltage switching and a switching loss reduces. Thereafter, the control unit waits until the voltage across the first switching element becomes zero or negative, and drives the first switching element on again.

  When the control unit transmits power from the second input / output terminal to the first input / output terminal, the voltage across the third switching element is zero or negative while the first and second switching elements are driven off. The third switching element is turned on. Thereafter, the third switching element is turned off while the fourth switching element is turned on, and the fourth switching element is turned on at least until the voltage across the third switching element increases in the positive direction and then returns to zero. Control to maintain the state. Also at this time, the switching loss of the third switching element can be reduced by the action of the second resonance capacitor.

  Since the first and second converter sections of this configuration only need to include two switching elements, the number of switching elements is reduced by half compared to the conventional full-bridge bidirectional converter. it can.

  According to the means of claim 2, the control unit transmits at least a period of time during which current flows from the flyback transformer to the second input / output terminal when transmitting power from the first input / output terminal to the second input / output terminal. In a part, the third switching element is turned on. When power is transmitted from the second input / output terminal to the first input / output terminal, the first switching element is turned on in at least part of a period in which current flows from the flyback transformer to the first input / output terminal. Thereby, synchronous rectification is performed, and the energization loss of the first and third switching elements can be reduced.

  According to a third aspect of the present invention, the first converter unit includes a smoothing circuit between the first input / output terminal and the flyback transformer, and the second converter unit includes the second input / output terminal and the flyback transformer. Is provided with a smoothing circuit. Thereby, the fluctuation | variation of the voltage between 1st input / output terminals and the voltage between 2nd input / output terminals can be suppressed.

  According to a fourth aspect of the present invention, a Schottky barrier diode is connected in antiparallel to each of the first to fourth switching elements. Since the forward voltage of the body diode of the switching element is relatively high, the conduction loss can be further reduced by connecting a Schottky barrier diode in parallel to the switching element.

  According to a fifth aspect of the present invention, the first voltage detection circuit for detecting the voltage between the first input / output terminals and the second voltage detection circuit for detecting the voltage between the second input / output terminals are provided. When transmitting power from the first input / output terminal to the second input / output terminal, the control unit controls the on-drive time of the first switching element so that the voltage detected by the second voltage detection circuit is equal to the target voltage. To do. When transmitting power from the second input / output terminal to the first input / output terminal, the control unit controls the on-drive time of the third switching element so that the voltage detected by the first voltage detection circuit becomes equal to the target voltage. To do. Thereby, PFM (Pulse Frequency Modulation) control is performed, and the conversion power is adjusted so that the voltage on the output side matches the target voltage.

  According to the sixth aspect of the present invention, an inverter is provided between at least one of the first input / output terminals and between the second input / output terminals. As a result, power can be transmitted to and from an AC power source such as a commercial power source.

  According to a seventh aspect of the present invention, the first to fourth switching elements are semiconductor elements using silicon carbide (SiC) or gallium nitride (GaN). Since these semiconductor elements have high breakdown voltage and low loss characteristics, the loss of the bidirectional flyback converter can be further reduced.

The block diagram of the bidirectional flyback converter which shows 1st Embodiment Waveform diagram FIG. 1 equivalent diagram showing the second embodiment FIG. 1 equivalent view showing the third embodiment FIG. 1 equivalent view showing the fourth embodiment

In each embodiment, substantially the same parts are denoted by the same reference numerals and description thereof is omitted.
(First embodiment)
Hereinafter, a first embodiment will be described with reference to FIGS. 1 and 2. The bidirectional flyback converter 1 shown in FIG. 1 includes both a DC power source E1 connected between the first input / output terminals 2p and 2n and a DC power source E2 connected between the second input / output terminals 3p and 3n. Power in the direction. As the DC power supplies E1 and E2, for example, a solar battery, a storage battery (including a vehicle), a fuel cell, and the like are assumed.

  A first converter unit 4 is provided on the first input / output terminal 2 (2p, 2n) side, and a second converter unit 5 is provided on the second input / output terminal 3 (3p, 3n) side. The 1st converter part 4 and the 2nd converter part 5 are connected via the flyback transformer 6 which has illustration coupling.

  Between the first input / output terminals 2p and 2n of the first converter section 4, one winding 61 of the flyback transformer 6 and the drain and source of the N-channel MOS transistor Q1 are connected in series. A series circuit of the first resonance capacitor C1 and the drain-source of the N-channel MOS transistor Q2 is connected in parallel with the transistor Q1.

  Similarly, between the second input / output terminals 3p and 3n of the second converter unit 5, the other winding 62 of the flyback transformer 6 and the drain and source of the N-channel MOS transistor Q3 are connected in series. Yes. A series circuit of the second resonance capacitor C2 and the drain-source of the N-channel MOS transistor Q4 is connected in parallel with the transistor Q3. These transistors Q1 to Q4 correspond to the first to fourth switching elements in the present invention. Parasitic diodes (body diodes) are formed in the transistors Q1 to Q4.

  Between the first input / output terminals 2p and 2n, a first voltage detection circuit 7 for detecting a voltage between the terminals is provided. Between the 2nd input / output terminals 3p and 3n, the 2nd voltage detection circuit 8 which detects the voltage between the said terminals is provided. The control unit 9 performs on / off drive control by applying a gate voltage to the transistors Q1 to Q4 so that the voltage between the terminals on the output side becomes equal to the target voltage.

  Next, an operation when power is transmitted from the first input / output terminal 2 side to the second input / output terminal 3 side will be described with reference to FIG. The same operation is performed when power is transmitted from the second input / output terminal 3 side to the first input / output terminal 2 side.

  The current I1 represents the current input from the DC power source E1 to the first converter unit 4 through the first input / output terminal 2, and the current I2 is the DC power source E2 from the second converter unit 5 through the second input / output terminal 3. Represents the current output to. The resonance current IC1 represents the current flowing through the first resonance capacitor C1, and the resonance current IC2 represents the current flowing through the second resonance capacitor C2. In any current, the direction shown in the figure is positive.

  The control unit 9 drives the transistor Q1 on during a period in which the drain-source voltage of the transistor Q1 (hereinafter simply referred to as voltage) is zero or negative with the transistors Q3 and Q4 being turned off. In the case shown in FIG. 2, the control unit 9 has a time when the resonance current IC1 becomes negative and the voltage of the transistor Q1 decreases to −Vf (Vf: forward voltage of the diode), and current starts to flow through the parasitic diode of the transistor Q1. The transistor Q1 is turned on at t2 and t7. At this time, since the transistor Q1 performs zero voltage switching and zero current switching, the switching loss of the transistor Q1 can be reduced.

  When the transistor Q1 is turned on, the current in the winding 61 of the flyback transformer 6 increases and energy is stored in the flyback transformer 6. The controller 9 controls the ON drive time of the transistor Q1 so that the voltage detected by the second voltage detection circuit 8 becomes equal to the target voltage. Based on this feedback control, control unit 9 drives transistor Q1 off at time t3.

  Since the resonance current IC1 flows through the first resonance capacitor C1, when the transistor Q1 is driven off, the transistor Q2 is kept on. While the transistor Q1 is on, the transistor Q2 may be on or off. In this embodiment, the transistor Q2 is always turned on.

  When the transistor Q1 is turned off at time t3, a positive current I2 flows through the winding 62 of the flyback transformer 6, and power is transmitted to the second input / output terminal 3 side. Further, a resonance current IC1 due to resonance between the leakage inductance existing in the winding 61 of the flyback transformer 6 and the first resonance capacitor C1 flows through the transistor Q2. The controller 9 needs to continue to drive the transistor Q2 at least until time t6 until the voltage of the transistor Q1 increases in the positive direction and then decreases and returns to zero. As described above, in this embodiment, the transistor Q2 is always turned on.

  The first resonant capacitor C1 has an effect of suppressing a sharp rise in the voltage of the transistor Q1 when the transistor Q1 is turned off. Thereby, the transistor Q1 becomes zero voltage switching, and the switching loss of the transistor Q1 can be reduced.

  The positive current I2 in the second converter unit 5 flows through the parasitic diode of the transistor Q3. Synchronous rectification is performed to reduce current loss at this time. That is, in at least a part of the period during which the current I2 flows from the flyback transformer 6 to the second input / output terminal 3 (period from time t3 to time t7) (here, the period from time t4 to time t5), the transistor Q3 is turned on. Thereafter, the control unit 9 waits until the voltage of the transistor Q1 becomes zero or negative as described above, and turns on the transistor Q1 again (time t7). When the transistor Q1 is turned on, the voltages of the transistors Q3 and Q4 rise.

  In the operation described above, the control unit 9 adjusts the conversion power by changing the width of the period T1. On the other hand, the width of the period T2 is constant depending on the resonance frequency determined from the leakage inductance of the winding 61 of the flyback transformer 6 and the capacitance of the first resonance capacitor C1. Therefore, PFM control is performed and control is performed so that the voltage between the second input / output terminals 3p and 3n matches the target voltage. As one practical numerical example, the frequency of the PFM control is 10 kHz to 200 kHz, and the resonance frequency corresponding to the period T2 is about 100 kHz.

  Since there is no surge due to leakage inductance, the breakdown voltage of the transistors Q2 and Q4 is lower than the breakdown voltage of the transistors Q1 and Q3. The currents flowing through the transistors Q1 and Q3 are main currents of the flyback transformer 6 necessary for power conversion, and the currents flowing through the transistors Q2 and Q4 are resonance currents. For this reason, the current flowing through the transistors Q1 and Q3 is larger than the current flowing through the transistors Q2 and Q4. Therefore, the element sizes of the transistors Q1 and Q3 are larger than the element sizes of the transistors Q2 and Q4.

  The maximum voltage applied to the transistors Q1 and Q3 is determined by the leakage inductance of the windings 61 and 62 of the flyback transformer 6 and the capacitance of the resonant capacitors C1 and C2. Since film capacitors, ceramic capacitors, etc. are used as the actual resonant capacitors C1 and C2, there are no high withstand voltage and large capacity capacitors. For this reason, considering the variation of applicable capacitors, the voltage applied to the transistors Q1 and Q3 is higher than the voltage of the DC power supplies E1 and E2 (for example, about 5 to 7 times). In particular, when the load is high and the frequency is low (T1 >> T2), the voltage applied to the transistors Q1 and Q3 increases.

Loss can be reduced by using high breakdown voltage and low loss semiconductor elements such as IGBT, SiC (silicon carbide), and GaN (gallium nitride) for the transistors Q1 to Q4. For example, when the power supply voltage E1 is 200V and the transistor Q1 requires a breakdown voltage of 2000V, which is ten times that due to resonance, the on-resistance of the Si MOS transistor is 1300 mΩcm ² (theoretical value), and the on-resistance of the SiC MOS transistor is 2 mΩcm ² (theoretical value). Therefore, by using the SiC MOS transistor, it is possible to greatly reduce the conduction loss of the element.

  By using the high breakdown voltage element, the surge voltage generated at the voltage across the transistors Q1 and Q3 can be absorbed even when the capacitance values of the resonance capacitors C1 and C2 are small, so that the resonance capacitors C1 and C2 can be downsized. Further, since SiC and GaN can be driven in a high frequency region as compared with the IGBT, the flyback transformer 6 can be downsized. When the flyback transformer 6 is downsized, the leakage inductance of the windings 61 and 62 is reduced. Therefore, the resonant capacitors C1 and C2 can also be reduced in size by reducing the capacitance value. Further, when the leakage inductance of the windings 61 and 62 is reduced, the width of the period T2 is shortened, so that the flyback transformer 6 can be further reduced in size.

  As described above, since the first and second converter units 4 and 5 of the bidirectional flyback converter 1 only need to include two transistors (switching elements), the conventional bidirectional converter having a full bridge configuration. Compared to the above, the number of transistors can be reduced to ½ and the size can be reduced. A high-breakdown-voltage and low-loss transistor is relatively expensive, so that the cost can be reduced.

  By changing the winding ratio of the flyback transformer 6, various voltages E1 and E2 can be handled. As a result, even when the voltage difference between the DC power supplies E1 and E2 is large, power can be transmitted. Further, as described above, since the transistors Q1 and Q3 are driven and controlled so as to perform zero voltage switching and zero current switching, the switching loss can be reduced and the efficiency can be increased. Furthermore, since the synchronous rectification is performed by turning on the transistor Q1 or Q3 in the converter section on the output side, the conduction loss of the transistor Q1 or Q3 can be reduced, and the efficiency can be further improved.

(Second Embodiment)
The bidirectional flyback converter 11 of the second embodiment shown in FIG. 3 includes a capacitor C3 corresponding to a smoothing circuit between the first input / output terminals 2p and 2n, and smoothes between the second input / output terminals 3p and 3n. A capacitor C4 corresponding to the circuit is provided. A low-pass filter is configured by the leakage inductance of the capacitor C3 and the winding 61 and the leakage inductance of the capacitor C4 and the winding 62, respectively. According to the present embodiment, fluctuations in the voltages E1 and E2 can be suppressed. In addition, operations and effects similar to those of the first embodiment can be obtained.

(Third embodiment)
The bidirectional flyback converter 21 of the third embodiment shown in FIG. 4 includes Schottky barrier diodes D1 to D4 in antiparallel with the transistors Q1 to Q4. Although a parasitic diode (body diode) is formed in the MOS transistor, the forward voltage of the parasitic diode formed in the SiC MOS transistor is compared with the forward voltage of the parasitic diode formed in the Si MOS transistor. large. Thus, by providing a Schottky barrier diode in parallel with the MOS transistor as in the present embodiment, the conduction loss of the transistors Q1 to Q4 can be reduced. In addition, operations and effects similar to those of the first embodiment can be obtained.

(Fourth embodiment)
The bidirectional flyback converter 31 of the fourth embodiment shown in FIG. 5 includes an inverter 32 between the second input / output terminals 3p and 3n of the bidirectional flyback converter 11 shown in FIG. The capacitor C3 shown in FIG. 3 may be provided as necessary. In FIG. 5, the description of the first voltage detection circuit 7 and the second voltage detection circuit 8 is omitted.

  The inverter 32 is a single-phase inverter composed of N-channel MOS transistors Q5 to Q8, and its input terminals 33p and 33n are connected to the second input / output terminals 3p and 3n, respectively. The output nodes N1 and N2 of each phase of the inverter 32 are connected to output terminals 35p and 35n via a reactor 34. The DC power supply E1 is, for example, a fuel cell, and the output terminals 35p and 35n are connected to an AC power supply, for example, a single-phase commercial power supply system (100V / 200V).

  According to this embodiment, bidirectional power transmission is possible between a DC power supply and an AC power supply. Instead of the above configuration, an inverter may be provided between the first input / output terminals 2p and 2n, and an inverter is provided between the first input / output terminals 2p and 2n and between the second input / output terminals 3p and 3n. Also good. The inverter may have a three-phase configuration.

(Other embodiments)
As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to embodiment mentioned above, A various deformation | transformation and expansion | extension can be performed within the range which does not deviate from the summary of invention.

The synchronous rectification described in the first embodiment may be performed as necessary.
In the second embodiment, a reactor is provided between the first input / output terminal 2p and the flyback transformer 6 and between the second input / output terminal 3p and the flyback transformer 6 while paying attention to an increase in surge voltage. May be. In the second embodiment, the first input / output terminals 2p, 2n of the first converter unit 4 and the flyback transformer 6 and the second input / output terminals 3p, 3n of the second converter unit 5 and the flyback transformer are used. 6 may be provided with smoothing circuits having configurations other than the capacitors C3 and C4.

In the fourth embodiment, the bidirectional flyback converter 1 or 21 and the inverter 32 may be combined instead of the bidirectional flyback converter 11.
The control of the output voltage is not limited to the feedback control described above, and may be open loop control. The first voltage detection circuit 7 and the second voltage detection circuit 8 may be provided as necessary.

  In the drawing, 1, 11, 21, 31 are bidirectional flyback converters, 2p, 2n are first input / output terminals, 3p, 3n are second input / output terminals, 4 is a first converter section, and 5 is a second converter section. , 6 is a flyback transformer, 7 is a first voltage detection circuit, 8 is a second voltage detection circuit, 9 is a control unit, 32 is an inverter, 61 is one winding, 62 is the other winding, and C1 is the first A resonant capacitor, C2 is a second resonant capacitor, C3 and C4 are capacitors (smoothing circuits), Q1 to Q4 are MOS transistors (first to fourth switching elements), and D1 to D4 are Schottky barrier diodes.

Claims (7)

A first converter section (4) provided on the first input / output terminal (2p, 2n) side, a second converter section (5) provided on the second input / output terminal (3p, 3n) side, the first converter A flyback transformer (6) for connecting the first converter unit and the second converter unit, and a control unit (9) for controlling the first converter unit and the second converter unit,
The first converter unit includes a first switching element (Q1) provided in series with one winding (61) of the flyback transformer between the first input / output terminals, and is parallel to the first switching element. A series circuit of a first resonance capacitor (C1) and a second switching element (Q2) provided in
The second converter unit includes a third switching element (Q3) provided in series with the other winding (62) of the flyback transformer between the second input / output terminals, and in parallel with the third switching element. Comprising a series circuit of a second resonant capacitor (C2) and a fourth switching element (Q4) provided in
When the controller transmits power from the first input / output terminal to the second input / output terminal, the voltage across the first switching element is zero while the third and fourth switching elements are driven off. The first switching element is turned on during a negative period, and then the first switching element is turned off in a state where the second switching element is turned on. At least the voltage across the first switching element is positive When the second switching element is controlled to be kept in an on state until it returns to zero after increasing the power to the first input / output terminal from the second input / output terminal, the first, The third switching element is turned on during a period in which the voltage across the third switching element is zero or negative while the second switching element is driven off. Then, the fourth switching element is turned on while the third switching element is turned off, and the fourth switching element is at least until the voltage across the third switching element increases in the positive direction and then returns to zero. A bidirectional flyback converter, wherein the switching element is controlled to be kept in an on state.   When the control unit transmits power from the first input / output terminal to the second input / output terminal, the control unit performs at least part of a period during which current flows from the flyback transformer to the second input / output terminal. 3 When the switching element is turned on and power is transmitted from the second input / output terminal to the first input / output terminal, at least a part of a period during which current flows from the flyback transformer to the first input / output terminal 2. The bidirectional flyback converter according to claim 1, wherein the first switching element is turned on.   The first converter unit includes a smoothing circuit (C3) between the first input / output terminal and the flyback transformer, and the second converter unit includes the second input / output terminal, the flyback transformer, A bidirectional flyback converter according to claim 1 or 2, further comprising a smoothing circuit (C4) between the two.   The bidirectional fly according to any one of claims 1 to 3, wherein Schottky barrier diodes (D1 to D4) are connected in antiparallel to the first to fourth switching elements, respectively. Buck converter. A first voltage detection circuit (7) for detecting a voltage between the first input / output terminals;
A second voltage detection circuit (8) for detecting a voltage between the second input / output terminals,
When the control unit transmits power from the first input / output terminal to the second input / output terminal, the control unit controls the first switching element so that the voltage detected by the second voltage detection circuit is equal to a target voltage. When the ON drive time is controlled and power is transmitted from the second input / output terminal to the first input / output terminal, the third switching is performed so that the voltage detected by the first voltage detection circuit becomes equal to the target voltage. The bidirectional flyback converter according to any one of claims 1 to 4, wherein an ON drive time of the element is controlled.   The bidirectional flyback converter according to any one of claims 1 to 5, further comprising an inverter (32) between at least one of the first input / output terminals and between the second input / output terminals. .   The bidirectional flyback according to any one of claims 1 to 6, wherein the first to fourth switching elements are made of a semiconductor element using silicon carbide (SiC) or gallium nitride (GaN). converter.

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