JPH0650946B2 - Series resonant converter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a series resonant converter capable of obtaining a DC voltage required for a load.

[Conventional technology]

The magnitude of the resonance current in the series resonance converter is determined by the inductance value of the resonance reactor, the capacitance value of the resonance capacitor, the DC input voltage and the DC output voltage. Therefore, much research has been conducted on the relationship between these values and the resonance current. According to these studies, in order to control the output voltage of the series resonant converter at a constant voltage without depending on the value of the output current, the magnitude of the output current (resonance current It is necessary to adjust the average value). However, when the series resonant converter is controlled by a constant voltage by frequency control, since the output current and the operating frequency are in a proportional relationship, the operating frequency drops to the audible range when the load is light (when the output current is small). However, there is a problem that noise is generated.

To solve this problem, a tank circuit consisting of a parallel resonant circuit whose impedance becomes infinite at the resonant frequency is inserted in the series resonant loop, and the impedance of the resonant loop is increased when the load is light, so that the operating frequency depends on the load. A series resonant converter has been proposed as shown in FIG.

The conventional series resonant converter will be described with reference to FIG.
Switch elements 11, 1 such as bipolar transistors
A first circuit 13 in which 2 is connected in series in the forward direction and a second circuit 1 in which diodes 14 and 15 are connected in series in the forward direction
A DC power supply 21 is connected between both ends of the circuit 6 and the third circuit 19 in which the resonance capacitors 17 and 18 are connected in series. The switch elements 11 and 12 are in the forward direction with respect to the DC power source 21, but the diodes 14 and 15 are in the reverse direction. The connection point of the diodes 14 and 15 and the connection point of the resonance capacitors 17 and 18 are connected to each other.
A fourth circuit 24 is connected between the connection point 23 of the switch elements 11 and 12. The fourth circuit 24 is a rectifier circuit 25.
And a resonance inductor 26 and a tank circuit 27 connected in series. The tank circuit 27 is composed of a resonance inductor 28 and a resonance capacitor 29 in parallel. The rectifier circuit 25 includes a bridge circuit of diodes 31 to 34,
An output capacitor 35 is connected between the output terminals, and a load 36 is connected in parallel with the output capacitor 35.

As an initial condition, the resonance capacitor 17 is the DC power supply 21.
The operation will be described on the assumption that the resonance capacitor 18 is discharged to zero voltage and the resonance capacitor 18 is discharged to zero voltage. When the semiconductor switch 11 is turned on in this state, the DC power supply 21 causes the semiconductor switch 11 → the diode 31 of the rectifier circuit 25
→ load 36 (capacitor 35) → diode 33 of the rectifier circuit 25 → inductor 26 for resonance → charging current i1 to the capacitor 18 for resonance flows through the tank circuit 27, and at the same time switch element 11 → diode 31 of the rectifier circuit 25 →
The discharge current i2 of the resonance capacitor 17 flows through the load 36 (capacitor 35) → the diode 33 of the rectifier circuit 25 → the resonance inductor 26 → the tank circuit 27. This current discharges the resonance capacitor 17, and the resonance capacitor 1
8 is the resonance current that charges the capacitor 8, and the capacitance Cp of the capacitor 29 of the tank circuit 27 is
(Or is set to be larger than the capacitor Cs of the resonance capacitor 18), the voltage of the output capacitor 35 (output voltage) is Vo and the inductor of the resonance inductor 26 is L.
s, if the voltage of the DC power supply 21 is Vi, then After that, the voltage of the resonance capacitor 17 becomes zero and the voltage of the resonance capacitor 18 becomes the power supply voltage Vi. At this moment, the diode 14 becomes conductive and the current flowing through the resonance inductor 26 is the resonance inductor 26 → tank circuit 27 → diode 14 → switch element 11 → rectifier circuit 25 → load 36.
(Capacitor 35) → Flows as a current i2 through the rectifier circuit 25. This current i2 is consumed by the load 36 and eventually becomes zero.

When the switching element 12 is turned on next after the half cycle of the operation is completed, the resonance capacitor 17 is charged and the resonance capacitor 18 is discharged, the same operation as described above occurs, and the next half cycle ends. .

The capacitance of the capacitor 29 of the tank circuit 27
Resonance frequency of Cp and inductance Lp of inductor 28 Is the capacitance Cs of the resonance capacitor 17 (or the capacitor 18) and the resonance inductor 26 inductance Ls.
Resonance frequency with Was set lower, the frequency f ₁ tank circuit in the near 27
The minimum value of the operating frequency is clamped to f ₀ by increasing the impedance of. In other words, the operating frequency is higher than the audible frequency so as not to give noise to the surroundings, and the operating frequency is reduced to reduce the output current, but the tank circuit 27 causes parallel resonance so that it can operate even at a light load. The current was limited to supply a small output current. By using such a tank circuit, it is possible to operate even under a light load without lowering the operating frequency to the audible frequency. Generally, in order to keep the output voltage or output current constant, the fluctuation is detected and the operating frequency is automatically controlled.

[Problems to be solved by the invention]

In such a conventional circuit, in order to transfer the desired energy to the output side, the resonance capacitor 29 of the tank circuit 27 has to have a capacitance 4 to 5 times larger than that of the resonance capacitor 17 or 18. The handling energy of the tank circuit 27 becomes large. Therefore, a large resonance inductor must be used, and power loss will increase. In addition, there is also a drawback that a large-capacity resonance capacitor must be separately provided for the tank circuit 27.

[Means and Actions for Solving Problems]

In order to eliminate such a defect of the conventional circuit, in the present invention, the resonance capacitor is shared by the series co-advance circuit and the parallel co-advance circuit, and the capacitance of the resonance capacitor is much larger than that of the conventional tank circuit. Since the size of the resonance inductor is small, the handling energy is small, and therefore, the resonance inductor can be downsized and the power loss can be reduced.

〔Example〕

An embodiment of the series resonant converter according to the present invention will be described with reference to FIG. In FIG. 1, parts corresponding to those in FIG. 3 are designated by the same reference numerals.

In this series resonance converter, the connection point between the diodes 14 and 15 of the second circuit 16 and the connection point between the resonance capacitors 17 and 18 of the third circuit 19 and the DC power supply 21 The resonance inductor 28 is provided between the point potential point B, the resonance capacitors 17 and 18 perform parallel resonance with the resonance inductor 28, and perform series resonance with the resonance inductor 26, respectively.
The main current flowing through the first circuit 13 is configured to flow through the third circuit 19.

The operation of this circuit is almost the same as that of the conventional circuit described above. Now, when the switch element 11 is turned on, the DC power supply 21
The switching element 11-the primary winding of the transformer 40-the inductor 26 for resonance-the charging current to the resonance capacitor 18 flows through the connection point A, and at the same time the switching element 11-the primary winding of the transformer 40-for resonance The discharge current of the resonance capacitor 17 flows through the inductor 26. This current is a resonance capacitor
After charging 18 to almost the power supply voltage and discharging the resonance capacitor 17 to almost zero voltage, the diode 14 of the second circuit 16 becomes conductive, and the energy stored in the resonance inductor 26 becomes diode 14-switch element 11 -Transmitted to the output side via the transformer 40.

Then, the switch element 12 is turned on after both the switch elements 11 and 12 have been turned off, but the ON operation of the switch element 12 is the same as that of the switch element 11, so the description thereof is omitted.

Since the diodes 14 and 15 are respectively connected in parallel with the resonance capacitors 17 and 18 of the third circuit 19, no adverse effects due to the recovery of the diodes 14 and 15 occur.

Even when both the switching elements 11 and 12 are off, the resonance capacitors 17 and 18 and the resonance inductor 28 oscillate at the peculiar parallel resonance frequency to oscillate the voltage at the connection point A. And switch element at light load
The voltage across 11 or 12 is small (DC power supply 21A or 21
In the voltage state of the connection point A exhibiting a voltage with a small amplitude obtained by subtracting the voltage of the connection point A from the voltage of B), the switching element 11
Alternatively, 12 is turned on to reduce the amplitude of the voltage applied to the primary winding of the transformer 40. The amplitude of the voltage oscillation at the connection point A increases as the switching frequency of the switch elements 11 and 12 approaches the parallel resonance frequency of the resonance capacitor 17 or 18 and the resonance inductor 28. Therefore, when the load is light, the switching element 11 or 12 is switched at a frequency close to the parallel resonance frequency.

Next, at the rated load, since the switching elements 11 and 12 are switched at a frequency considerably higher than the parallel resonance frequency, the amplitude of voltage oscillation at the connection point A is small. Therefore,
The amplitude of the voltage value obtained by subtracting the voltage at the connection point A from the voltage of the DC power supply 21A or 21B is large, and the voltage applied to the primary winding of the transformer 40 is large.

Next, referring to FIG. 2, an embodiment of the series resonance converter according to the present invention will be described. In this embodiment, the DC power supply 21 is composed of a three-phase full-wave rectifier 21 ', a choke 43, and capacitors 41 and 42. . Capacitors 41 and 42 form a choke 43 and a filter, and apply a voltage of approximately half the DC power supply voltage to the midpoint potential point B thereof. Normally, the capacitors 41 and 42 are designed to have a capacitance 10 times or more larger than that of the resonance capacitor 17 or 18, and do not substantially affect resonance.

〔The invention's effect〕

As described above, according to the present invention, two relatively stable DC voltage sources are provided on the input side, and the resonance capacitor is shared by the parallel resonance circuit and the series resonance circuit. Since it is much smaller than the capacitance of the resonance capacitor of the tank circuit, the amount of energy that can be handled can be made sufficiently small. Therefore, it is not necessary to separately provide a resonance capacitor for the parallel resonance circuit, and it is stable. The resonance inductor can be downsized, and the power loss can be reduced.

[Brief description of drawings]

1 and 2 are views showing different embodiments of the series resonance converter according to the present invention, and FIG. 3 is a view for explaining a conventional series resonance converter. 11,12 ...... Main switch element 13 ...... First circuit 14,15 ...... Diode 16 ...... Second circuit 17,18 ...... Resonance capacitor 19 ...... Third circuit 21 ...... DC current 26, 28 …… Resonance inductor 40 …… Transformer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Japanese Patent Laid-Open No. 1-234052 (JP, A)

Claims (2)

[Claims] 1. A first circuit in which a first switch element and a second switch element are connected in series in a forward direction with each other, and a first circuit in which a first diode and a second diode are connected in series with each other in a forward direction. The second circuit, the third circuit in which the first resonance capacitor and the second resonance capacitor are connected in series, the connection point between the first switch element and the second switch element, and the first circuit Of the first switching element or the second switching element flowing between the connection point between the second diode and the second diode and the connection point between the first resonance capacitor and the second resonance capacitor. A first resonance inductor connected to a current path, a first direct current power supply and a second direct current power supply are connected in series, and the first circuit, the second circuit and the third circuit are connected. It is connected between both ends and A connection point between the first DC power supply and the second DC power supply, a connection point between the first diode and the second diode via a second resonance inductor, the first resonance capacitor, and A series resonance converter comprising a DC power supply coupled to a connection point of a second resonance capacitor. 2. A first circuit in which a first switch element and a second switch element are connected in series in the forward direction, and a first circuit in which a first diode and a second diode are connected in series in the forward direction. 2 circuit, a third circuit in which a first resonance capacitor and a second resonance capacitor are connected in series, a connection point of the first switch element and the second switch element, and the first circuit Between the connection point of the diode and the second diode and the connection point of the first resonance capacitor and the second resonance capacitor, the main current flowing through the first switch element or the second switch element A first resonance inductor connected to the passage, a rectifying device, and a large capacitance for giving two relatively stable DC voltages and having substantially no effect on resonance. A direct current power supply comprising a pair of capacitors connected in series, a connection point of the first diode and the second diode, a connection point of the first resonance capacitor and the second resonance capacitor, and A series resonance converter, comprising a second resonance inductor connected between the DC power supply and the connection point between the capacitors.