JP5169679B2 - Resonant power converter - Google Patents

Description

  The present invention relates to a resonant power converter using a semiconductor switching element, and more particularly to a resonant power converter suitable for reducing loss.

FIG. 6 shows a conventional resonant power converter (resonant DC-DC converter). Reference numeral 1 denotes a DC voltage source. The DC voltage source 1 includes a series circuit (first series circuit) in which first and second switching elements (MOSFETs (Q ₁ , Q ₂ )) are connected in series, and third and fourth switching elements ( A series circuit (second series circuit) in which MOSFETs (Q ₃ , Q ₄ )) are connected in series is connected in parallel. These MOSFETs (Q _{1 to} Q ₄ ) have parasitic diodes D _{1 to} D ₄ , respectively. Capacitors C _{1 to} C ₄ are connected in parallel between the drain and source of the MOSFETs (Q _{1 to} Q ₄ ), respectively.

MOSFET _{(Q 1)} source and a connecting point a drain are connected to each of the MOSFET _{(Q 2)} of, MOSFET _{(Q 3)} source and MOSFET drain and is the connection point b, which is connected to _{(Q 4)} of A series circuit (third series circuit) in which the reactor L _s , the capacitor C _s, and the primary winding of the transformer T are connected in series is connected between them. The reactor L _s and the capacitor C _s serve as a series resonance circuit for performing a current resonance operation.

The secondary winding of the transformer T includes a center tap. Two rectifier diode cathodes (D ₅ , D ₆ ) to which the respective cathodes are connected are connected to both ends of the secondary winding of the transformer T to form a full-wave rectifier circuit. A smoothing capacitor C is connected to the DC output side of the full-wave rectifier circuit, that is, between the center tap of the transformer T and the anode of the rectifier diodes (D ₅ , D ₆ ) to constitute the converter 4. The DC output voltage of converter 4 is applied to load _RL .

In the conventional resonance type DC-DC converter configured as described above, when both the MOSFET (Q ₁ ) and the MOSFET (Q ₄ ) are turned on by a switching element driving unit (gate driving unit) (not shown), the connection point a And the voltage V _ab between the connection point b and the connection point b become positive. Next, when the gate driver turns off both the MOSFET (Q ₁ ) and the MOSFET (Q ₄ ) and turns on both the MOSFET (Q ₂ ) and the MOSFET (Q ₃ ), V _ab becomes a negative voltage.

The resonant DC-DC converter generates an alternating voltage by alternately performing this operation, and applies it to the primary winding of the transformer T. Then, the AC voltage that is insulated and transformed through the transformer T and appears on the secondary winding side of the transformer T is rectified by the rectifying diodes D ₅ and D ₆ so that a desired DC output voltage is obtained. It has become.
In FIG. 7 showing an example of the voltage / current waveform of each part of the resonance type DC-DC converter configured as described above, the MOSFETs (Q ₂ , Q ₃ ) that are switched from on to off at time t ₁ are these MOSFETs. voltage applied by the capacitor _C 2, _{C 3} between the source MOSFET _(Q 2, Q ₃₎ is turned off before the rising - _(Q 2, _{Q 3)} the drain of. For this reason, the MOSFETs (Q _{1 to} Q ₄ ) are zero-voltage switching, and almost no loss (turn-off loss) is generated at the time of turn-off.

Here, Vgs _{1 to} Vgs ₄ in FIG. 7 are the gate-source voltages of the MOSFETs (Q _{1 to} Q ₄ ), I _p and V _p are the current flowing through the primary winding of the transformer T and the applied voltage, V ₃ and _I 3, _{V 4} and _{I 4,} the drain of the MOSFET, respectively _{(Q 3)} - is a source current - source voltage and drain - drain-source current, MOSFET _{(Q 4)} - source voltage and the drain .

The drain of the MOSFET _(Q 1 ~Q ₄₎ - capacitor _C 1 _-C 4 which are respectively connected between the source may also be able to substitute the parasitic capacitance of the MOSFET _(Q 1 ~Q _4). In this case, these capacitors C _{1 to} C ₄ can be omitted.
Further, the MOSFETs (Q ₁ , Q ₄ ) that are switched from OFF to ON at time t ₂ in FIG. 7 are turned on when a current flows through the parasitic diodes D ₁ and D ₄ , so that no turn-on loss occurs.

  The DC voltage source 1 shown in FIG. 6 is generally obtained by rectifying a commercial AC power source with a converter, although not particularly shown. In this commercial AC power supply, a so-called instantaneous voltage drop (instantaneous drop) that occurs immediately after the voltage drops for a short time rarely occurs. When the load is an electronic control unit, it may be affected by this voltage fluctuation. Therefore, it is necessary to keep the output voltage of the DC-DC converter constant even when a sag occurs.

Therefore resonant DC-DC converter of this kind, when the input voltage is lowered by voltage sag, to maintain the DC output voltage V _o constant, MOSFET as shown in the operation waveform of each part of FIG. 8 (Q ₁ to Q ₄₎ is lower than the steady state switching frequency of. Then, the resonance impedance of the series resonance circuit composed of the reactor L _s and the capacitor C _s decreases, and the amount of power transmitted to the transformer T, that is, the amount of power transmitted to the DC output side can be maintained, and the DC output voltage can be maintained. The voltage can be maintained at a predetermined voltage (note that the reference numerals in FIG. 8 have the same meaning as in FIG. 7).

In the resonant DC-DC converter that operates as described above, the circuit parameters are set so that the DC output voltage can be kept constant even when an instantaneous drop occurs in the commercial AC power supply. That is, during normal times, the output is reduced by increasing the resonance impedance of the series resonance circuit by operating at a higher frequency.
Therefore, the conventional resonant DC-DC converter is
(1) Since the power factor decreases, the ineffective component of the current increases and the conduction loss increases. (2) The core loss of the reactor increases due to the increase in frequency. (3) The drive loss of the switching element increases. Arise.

These become more remarkable as the switching frequency is increased. In addition, the problem (3) is particularly significant in a low-capacity power supply in which the ratio of driving power is large.
As a method for solving these problems, a method has been proposed in which an alternating voltage (corresponding to V _ab ) obtained by switching a circuit from a half-bridge operation to a full-bridge operation at the time of a sag is increased (for example, Patent Document 1, 2).
JP-A-10-243649 Japanese Patent Laid-Open No. 2004-112925

  However, the methods described in Patent Documents 1 and 2 have a problem that the output voltage is likely to fluctuate due to the switching operation. In addition, the voltage applied to the primary winding of the transformer T during half-bridge operation is half that during full-bridge operation. Therefore, in order to obtain the same output power, the primary current is compared with the full-bridge operation. There is also a problem that the conduction loss increases due to the increase in current.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a resonant power converter that can maintain a constant output voltage even during a sag, while reducing loss. Is to provide.

  In order to achieve the above-described object, a resonant power converter according to the present invention includes a first series circuit connected to a DC voltage source and connected in series with first and second switching elements, and the first series circuit. A second series circuit connected in parallel with the circuit and having the third and fourth switching elements connected in series; a connection point of the first and second switching elements; and the third and fourth switching elements. And a third series circuit connected in series with the reactor, the capacitor, and the primary winding of the transformer, and a predetermined series connected to the secondary winding of the transformer. A resonance type power converter that supplies power to a load, wherein the first series circuit uses a switching element having a lower forward voltage drop than the second series circuit.

  The resonance type power converter is connected in parallel to the DC voltage source, detects a voltage value of the DC voltage source, receives the detected voltage value of the voltage detector, and receives the DC voltage source. Is outputting a voltage equal to or higher than a predetermined voltage value, only one of the first and second switching elements is always on and the other is always off, and the third and fourth switching elements Is exclusively turned on or off at a predetermined cycle, while the third and fourth switching elements are excluded at the predetermined cycle when the DC voltage source outputs a voltage less than a predetermined voltage value. The first and second switching elements are exclusively turned on or off at the predetermined period, and the on or off time is adjusted to provide the third series circuit. Join Configured with a switching element driving unit sustaining a voltage to a predetermined voltage value.

In the resonant power converter, when the DC voltage source outputs a voltage equal to or higher than a predetermined voltage value, the first or second switching element that is always turned on by the switching element driving unit is other than The switching element has a lower forward voltage drop than that of the switching element.
Furthermore, when the DC voltage source outputs a voltage equal to or higher than a predetermined voltage value, the third or fourth switching element that is always turned off by the switching element driving unit is a switching element that is always turned on. It is assumed that the power capacity is smaller than that.

  You may comprise the secondary winding of the said transformer of the said resonance type | mold power converter device by providing the rectifier circuit which converts the alternating voltage produced in this secondary winding into a direct voltage.

The above-described resonant power converter includes first and second switching elements having a lower forward voltage drop than a second series circuit in which third and fourth switching elements connected to a DC voltage source are connected in series. Therefore, the conduction loss caused by the current flowing through the first series circuit can be reduced.
In addition, the above-described resonance type power converter uses, for example, a direct current obtained by rectifying a commercial AC power supply with a converter as a DC voltage source. And driving the third and fourth switching elements constituting the second series circuit, and at the time of a sag, further switching the first and second switching elements constituting the first series circuit to the optimum switching described above. Since the voltage applied to the third series circuit is maintained at a predetermined voltage value by driving at the frequency and adjusting the ON or OFF time, the increase in the loss described above is prevented, and even at the time of a sag. The DC output voltage can be kept constant.

In the resonant power converter according to the present invention, when the DC voltage source outputs a voltage equal to or higher than a predetermined voltage value, the first or second switching element is always turned on by the switching element driving unit. Since an element having a lower forward voltage drop than other switching elements is used, loss can be reduced and the apparatus can be downsized.
Further, when the DC voltage source outputs a voltage equal to or higher than a predetermined voltage value, the first or second switching element that is always turned off by the switching drive unit is only when the DC voltage source is instantaneously reduced. Since it only needs to be driven, a device having a smaller power capacity than a switching element that is always turned on can be applied, and the device can be reduced in size and cost.

  In addition, the secondary winding of the transformer in the resonant power converter according to the present invention includes a rectifier circuit that converts an AC voltage generated in the secondary winding into a DC voltage, thereby suppressing power loss. In addition, it is possible to achieve a great practical effect such that a resonant DC-DC converter that can be reduced in size and price can be configured.

  Hereinafter, a resonant power converter according to an embodiment of the present invention will be described with reference to the accompanying drawings. 1 to 5 relate to one embodiment of the present invention, and the present invention is not limited by these drawings. Also, in these drawings, the portions denoted by the same reference numerals as those in FIGS. 6 to 8 represent the same items, and the basic configuration is the same as that of the conventional one shown in these drawings, and the description thereof will be omitted.

FIG. 1 is a diagram showing a schematic configuration of a resonant DC-DC converter to which a resonant power converter according to the present invention is applied. In this figure, reference numeral 10 denotes a voltage detector for detecting the voltage value of the DC voltage source 1. The voltage value detected by the voltage detection unit 10 is given to a gate driving unit (switching element driving unit) 11 that controls driving of the MOSFETs (Q _{1 to} Q ₄ ). Although not shown in FIG. 1, the gate driver (switching element driver) 11 is connected to each gate of the MOSFETs (Q _{1 to} Q ₄ ) and controls the driving thereof.

In general, in the resonant DC-DC converter configured as described above, when the voltage detection unit 10 detects that the DC voltage source 1 is at a voltage equal to or higher than a predetermined voltage value (normal time), the gate As shown in the operation waveform of each part in FIG. 2, the drive unit 11 always turns on the MOSFET (Q ₁ ) of the first series circuit and always turns off the MOSFET (Q ₂ ), thereby forming the second series circuit. The MOSFETs (Q ₃ , Q ₄ ) are switched on / off alternately (exclusively) at a predetermined cycle. At this time, since the MOSFET (Q ₁ ) is always on, V _ab = V _in when the MOSFET (Q ₄ ) is on, and V _ab = 0 when the MOSFET (Q ₃ ) is on.

V _{ab including} the DC component obtained at this time becomes an alternating voltage from which the DC component is removed by the capacitor C _s , and a voltage V _p corresponding to the alternating voltage is applied to the primary winding of the transformer T. . This voltage _Vp is insulated and transformed via the transformer T and appears as an AC voltage in the secondary winding of the transformer T. AC voltage appearing on the secondary winding to be rectified by the rectifying diode D _5, D ₆ is converted to direct current, DC output voltage V _o is applied to the load is smoothed by further smoothing capacitor C.

When the voltage drop occurs in the DC voltage source 1, the voltage detector 10 detects this voltage drop. Then, the gate driving unit 11 receives this voltage drop detection, and further adds the MOSFETs (Q ₁ , Q ₂ ) in addition to the MOSFETs (Q ₃ , Q ₄ ) as shown in the operation waveforms of the respective parts in FIG. with turning on or off alternately (exclusive) in a predetermined cycle, performing off-time control of the MOSFET on-time and MOSFET _{(Q 2)} of the _{(Q 1)} (pulse width control).

Here, a constant voltage value V _in of the DC voltage source 1 in order to simplify the description of the control of the pulse width. Since may newly have the level of + V _in the V _ab When you turn on MOSFET (Q ₁₎ as shown in FIG. 4, the fundamental wave component of V _ab (excluding the DC component) is higher than the steady state Become. Here, if the ON time of the MOSFET (Q ₁ ) is gradually increased, the effective value of V _p increases. When the duty finally reaches the maximum, ± V _in is applied to the primary winding of the transformer T as the voltage V _p , so that an output voltage value that is twice that in the steady state is obtained.

However, although actually V _in is reduced by voltage sag, it can be its voltage drop to obtain the same DC output voltage and a steady state to be less than half the steady state.
Note that the MOSFET (Q ₁ ) is always turned on by the gate driving unit 11 at a steady time. For this reason, switching loss is not a problem. Further, since the MOSFET (Q ₂ ) is always fixed off at the time of steady state, no loss occurs. In the first series circuit composed of MOSFETs (Q ₁ , Q ₂ ), the elements that are always on or always off may be replaced.

In general, the slower the switching speed, the lower the forward voltage drop when conducting. Therefore, a conduction loss during normal operation can be reduced in an element that is always on. Further, even if the performed switching MOSFET _{(Q 1)} MOSFET well _{(Q 2)} when the instantaneous drop, the driving of these MOSFET _(Q 1, Q ₂₎ is the normal operation for limited when only sag The loss of does not increase. In addition, when the DC voltage source 1 outputs a voltage equal to or higher than a predetermined voltage value, one of the switching elements of the MOSFET (Q ₁ ) or the MOSFET (Q ₂ ) that is always turned off by the gate driving unit 11 Since the power is turned on only at a low time, the power capacity may be smaller than that of the switching element that is always turned on.

In the resonant DC-DC converter shown in FIG. 1, capacitors C _{1 to} C ₄ are connected in parallel between the drains and sources of the MOSFETs (Q _{1 to} Q ₄ ) to perform zero voltage switching. The loss generated at this time varies depending on the capacitance values of these capacitors C _{1 to} C ₄ .
For example, as shown in FIG. 5, as the capacitance value increases from C = 0 (solid line in FIG. 5) when the MOSFET is turned off, the slope of the voltage decreases (from the alternate long and short dash line). That is, the turn-off loss determined by the product of the voltage value and the current value decreases as the capacitance value increases. However, if the capacitance values of the capacitors C _{1 to} C ₄ are too large, the power flowing into and out of the capacitors C _{1 to} C ₄ increases. In this case, care must be taken because the charge / discharge loss associated with the inflow / outflow of power may increase. Note that the capacitors C _{1 to} C ₄ may be omitted if the switching loss is sufficiently suppressed only by the parasitic capacitance of the MOSFETs (Q _{1 to} Q ₄ ).

Thus, in the resonant power converter according to the present invention, when a sag occurs in the DC voltage source 1, the gate drive unit (switching element drive unit) 11 causes the MOSFET (Q ₃ , Q ₄ ) to have an optimum switching frequency at the normal time. Further, MOSFETs (Q ₁ , Q ₂ ) having a lower forward voltage drop than these MOSFETs are driven at this switching frequency, and the ON or OFF time thereof is adjusted so that the primary winding of the transformer T Since the applied voltage is maintained at a predetermined voltage value, the secondary voltage (output voltage) of the transformer T can be kept constant even during a sag while preventing an increase in circuit loss.

In particular, in the resonance type power supply device of the present invention, the MOSFET (Q ₁ ) or the MOSFET (Q ₂ ) that is always turned off by the gate drive unit 11 when the DC voltage source 1 outputs a voltage equal to or higher than a predetermined voltage value. Is driven only when the voltage drops for a moment, a device having a smaller power capacity than a switching element that is always on can be applied, and the resonant power supply can be reduced in size and price.

In this embodiment, the MOSFET (Q ₁ ) is always turned on, but any one switching element of the MOSFETs (Q ₁ , Q ₂ ) constituting the first series circuit is always turned on, and the other is always turned off. Therefore, the present invention is not limited to the driving method described above.
Further, the resonance type power supply apparatus of the present invention is not limited to the resonance type DC-DC converter in which a full-wave rectifier circuit using a center tap is connected to the secondary side of the transformer T as described above. For example, the circuit connected to the secondary side of the transformer may be a resonant DC-DC converter having a full bridge rectifier circuit, a half bridge rectifier circuit, or the like. Or the resonance type power supply device of the present invention can of course be applied as a high frequency inverter to various power supply devices such as a plasma power supply device, an ozone generator, and an arc welding machine.

The schematic circuit diagram which shows an example of the resonance type DC-DC converter to which the power converter device of this invention is applied. The figure which shows the voltage and current waveform of each part at the normal time in the resonance type DC-DC converter shown in FIG. The figure which shows the voltage and electric current waveform of each part at the time of the instantaneous drop in the resonance type DC-DC converter shown in FIG. The figure which shows the voltage and electric current waveform of each part which changes with the magnitude | size of the voltage drop at the time of the voltage drop in the resonance type DC-DC converter shown in FIG. The figure which shows the waveform of the voltage and current at the time of turn-off when changing the electrostatic capacitance of the capacitor | condenser connected in parallel between the drain-source of MOSFET. The schematic circuit diagram which shows an example of the conventional resonance type DC-DC converter. The figure which shows the voltage and current waveform of each part at the normal time in the resonance type DC-DC converter shown in FIG. The figure which shows the voltage and electric current waveform of each part at the time of the instantaneous drop in the resonance type DC-DC converter shown in FIG.

Explanation of symbols

1 DC voltage source 4 converter 10 voltage detection unit 11 a gate driver C smoothing capacitor C _s capacitor D ₁ -D ₄ parasitic diode D _{5, D 6} rectifying diode L _s reactor R _L load T transformer

Claims (5)

A first series circuit connected to a DC voltage source and connecting the first and second switching elements in series;
A second series circuit connected in parallel with the first series circuit and having the third and fourth switching elements connected in series;
First connected to the connection point of the first and second switching elements and the connection point of the third and fourth switching elements, the reactor, the capacitor and the primary winding of the transformer connected in series 3 series circuits,
A resonant power converter for supplying power to a predetermined load connected to a secondary winding of the transformer,
The resonance power converter according to claim 1, wherein the first series circuit uses a switching element having a lower forward voltage drop than the second series circuit. A voltage detector connected in parallel to the DC voltage source and detecting a voltage value of the DC voltage source;
In response to the detection voltage value of the voltage detection unit, when the DC voltage source outputs a voltage higher than a predetermined voltage value, only one of the first switching element and the second switching element is always turned on. The other is always off, and the third and fourth switching elements are exclusively turned on or off in a predetermined cycle,
When the DC voltage source outputs a voltage less than a predetermined voltage value, the third and fourth switching elements are exclusively turned on or off at the predetermined period, and the first and second A switching element driving unit that exclusively turns on or off the switching element at the predetermined period and adjusts the on or off time to maintain the voltage applied to the third series circuit at a predetermined voltage value; The resonance type power converter according to claim 1, further comprising:   When the DC voltage source outputs a voltage equal to or higher than a predetermined voltage value, the first or second switching element, which is always turned on by the switching element driving unit, is more forward voltage than other switching elements. The resonant power converter according to claim 2, which has a low drop.   When the DC voltage source outputs a voltage equal to or higher than a predetermined voltage value, the first or second switching element that is always turned off by the switching element driving unit is a switching element that is always turned on. 3. The resonance type power converter according to claim 2, wherein the power capacity is small.   The resonance according to any one of claims 1 to 4, wherein the secondary winding of the transformer is provided with a rectifier circuit that converts an AC voltage generated in the secondary winding into a DC voltage. Type power converter.

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