JP2701172B2 - Resonant converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a resonant converter for obtaining a stabilized DC voltage from an AC power supply.

In a converter that applies a stabilized DC voltage from an AC power supply to a DC load, the AC voltage of the AC power supply is rectified, and the rectified output voltage is applied to the primary winding of the transformer via a switching element such as a transistor. Rectifying and smoothing the induced voltage of the secondary winding of the transformer by a rectifying and smoothing circuit to obtain an output DC voltage, and controlling the switching element so that the output DC voltage becomes a set value; Various configurations have already been proposed. In such converters, improvements in efficiency and power factor are desired.

[Conventional technology]

The conventional converter has, for example, the configuration shown in FIG. 6, in which 31 is an AC power supply, 32 is a full-wave rectifier circuit, 33 is a capacitor, 34 is a transformer, 35 is a transistor as a switching element, and 36 is a rectifier. A smoothing circuit 37 is a control circuit.

Transistor 35 is connected to the primary winding of transformer 34,
A rectifying / smoothing circuit 36 is connected to the secondary winding. The rectifying / smoothing circuit 36 is shown as being composed of diodes 38 and 39 and a capacitor 41 of the reactor 40. AC power supply 31
The AC voltage is rectified by the full-wave rectifier circuit 32 and charged in the capacitor 33, and the smoothed voltage is applied to the primary winding of the transformer 34 via the transistor 35, and is applied to the secondary winding of the transformer 34. The induced voltage is rectified and smoothed by the rectifying / smoothing circuit 36 to become an output DC voltage. This output DC voltage is compared with the set voltage in the control circuit 37, and the ON period of the transistor 35 is controlled in accordance with the error, so that the output DC voltage is stabilized.

7A and 7B are explanatory diagrams of voltage and current. FIG. 7A shows waveforms of a full-wave rectified output voltage 42 and a terminal voltage 43 of a capacitor 33, and FIG. And The sine-wave AC voltage is rectified by the full-wave rectifier circuit 32, resulting in a large pulsating voltage.
As a result, a rectified output voltage having a waveform 43 is obtained. In this case, the charging current 44 flows through the capacitor 33 only during a relatively short period (conduction angle) of t1 in the half cycle t of the AC voltage, and becomes zero during the remaining period t2. In this case, the average value of the charging current 44 needs to be equal to the DC output current 45. Therefore, the peak value of the charging current 44 increases as the conduction angle t1 decreases.

[Problems to be solved by the invention]

As described above, when the conventional capacitor-input type rectified power supply is used, the charging current flowing through the capacitor 33 flows only for a relatively short period t1, as shown in FIG. 7 (b). The power factor as seen from the power supply 31 side is very poor. The power factor co of a distorted wave with a waveform different from such a sine waveform
sθ is It can be expressed as. V ₀ , I ₀ are the voltage and current of the DC component, V ₁ , I ₁ , V ₂ , I ₂ , V ₃ , I ₃ ...
The voltage and current of the third harmonic,..., Θ ₁ , θ ₂ , θ ₃ ,.
Indicates the phase angle between the voltage and current of each harmonic.

Therefore, when a current having a distorted waveform as shown in FIG. 7B flows, as compared with the case where a sine wave current flows,
Is the waveform with little DC component and fundamental wave component or power factor cosθ
Becomes smaller. In the case of a conventional capacitor input type rectified power supply, the power factor cos θ is about 45 to 60%.

In order to reduce the peak value of the charging current of the capacitor 33, a choke-input type rectified power supply in which a choke coil is connected between the full-wave rectifier circuit 32 and the capacitor 33 may be used. However, in the case of this choke input type, the rectified output voltage is the average value of the pulsating voltage, so it is about 0.9 times the effective value of the input voltage. Has the disadvantage of rising. Further, in order to improve such disadvantages, it is necessary to increase the inductance of the choke coil considerably. In that case, a large choke coil is used, so that there is a disadvantage that the size is increased.

Therefore, in order to reduce the size, a capacitor input type rectified power supply is more often used than a choke input type rectified power supply.

In addition, the transistor 35 has a switching loss due to the time until it is completely turned on or off,
It is conceivable to reduce the size of the transformer 34 and the rectifying / smoothing circuit 36 by setting the switching frequency to a high frequency of about 1 MHz or more, but the switching loss increases almost in proportion to the increase in the switching frequency, and the temperature rise due to the loss From the point of view, it is difficult to achieve a desired high frequency.

Therefore, there has been proposed a resonance type converter that performs switching at a timing at which a current or a voltage becomes zero by utilizing resonance characteristics. In such a resonant converter, a variable frequency control method is used to stabilize the output DC voltage.

However, in this variable frequency control method, the frequency change range from no load to maximum load is several tens KHz.
Since the frequency must be set to several MHz and a circuit constant corresponding to the lowest frequency is determined, there is a disadvantage that downsizing is difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide a resonance type converter that can be easily reduced in size and frequency and has a high power factor.

[Means for solving the problem]

Referring to FIG. 1, the resonant converter of the present invention applies a full-wave rectifier circuit 1 for rectifying an AC voltage of an AC power supply such as a commercial power supply, and applies a rectified output voltage of the full-wave rectifier circuit 1. A connection point between the switching elements 4 and 5 including the first and second capacitors 2 and 3 connected in series and the first and second transistors connected in series, and the first and second capacitors 2 and 3 connected in series And a connection point between the first and second switching elements 4 and 5 connected in series, a capacitor 8 and a reactor 6 having a smaller capacity than the first and second capacitors 2 and 3 are connected. A resonance circuit connected in series, a transformer 7 having a primary winding connected in parallel with the capacitor 8 of the resonance circuit, a rectifying and smoothing circuit 9 connected to a secondary winding of the transformer 7, 1, resonance frequency switching frequency to control the second switching elements 4 and 5 alternately Set higher than the resonance frequency to control the switching frequency in response to the load, in which the output DC voltage of the rectifying and smoothing circuit 9 is constructed from stabilized to order control circuit 10 Metropolitan of.

[Action]

The rectified output voltage of the full-wave rectifier circuit 1 is applied to the primary winding of the transformer 7 via the second capacitor 3 and the reactor 6 when the first switching element 4 is turned on.
Is applied to the primary winding of the transformer 7 via the first capacitor 2 and the reactor 6 when the switching element 5 is turned on. Therefore, the first and second capacitors 2 and 3 function for DC cutoff, and perform functions different from those of the capacitors in the capacitor input type rectified power supply.

In addition, a resonance current mainly flows through the first and second switching elements 4 and 5 by a resonance circuit mainly including the reactor 6 and the capacitor 8, and switching can be performed at a point where current or voltage is zero. . Therefore, the switching loss can be made negligible.

The control circuit 10 controls the first and second switching elements 4 and 5 so as to stabilize the output DC voltage of the rectifying / smoothing circuit 9, and performs switching control at a frequency higher than the resonance frequency. By reducing the switching frequency as the output DC current increases, and setting the switching frequency to substantially the resonance frequency in the case of the rated load, switching of zero current or zero voltage can be performed, and switching loss can be eliminated.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a main part circuit diagram of an embodiment of the present invention. As described above, the AC voltage of the AC power supply 11 is rectified by the full-wave rectifier circuit 1, and the rectified output voltage is connected to the first and second series-connected rectifiers. The voltage is applied to the second capacitors 2 and 3 and the first and second switching elements 4 and 5 connected in series, and the connection point of the first and second capacitors 2 and 3 is connected to the first and second switching elements. A primary winding of a transformer 7 is connected between the connection points of the elements 4 and 5 via a reactor 6, and a capacitor 8 is connected in parallel with the primary winding to form a resonance circuit with the reactor 6. The output DC voltage of the rectifying / smoothing circuit 9 connected to the secondary winding of the transformer 7 is monitored by the control circuit 10 so that the set voltage is obtained.
It controls the first and second switching elements 4 and 5.

Also, a case is shown in which the secondary winding of the transformer 7 has a configuration having a center tap.
Shows a case where the circuit is composed of the diodes 12 and 13 and the capacitor 14. The switching elements 4 and 5 use field-effect transistors, and have parasitic diodes 15 and 16 and a parasitic capacitance 1.
Shows the case with 7,18. The parasitic capacitances 17, 18 can be external capacitors.

Then, when the first switching element 4 is turned on,
A current flows from the full-wave rectifier circuit 1 through the path of the first switching element 4 → the capacitor 8 → the reactor 6 → the second capacitor 3. At this time, the charge of the first capacitor 2 is discharged. When the second switching element 5 is turned on, a current flows from the full-wave rectifier circuit 1 through the path of the first capacitor 2 → the reactor 6 → the capacitor 8 → the second switching element 5, and at this time, the second capacitor 3 is discharged. Then, a current according to the voltage at both ends of the capacitor 8 flows through the primary winding of the transformer 7 connected to both ends of the capacitor 8.

If the first and second capacitors 2 and 3 are, for example, 28.8 μF, the series capacitor 8 of the reactor 6 is 0.4 μF, and the reactor 6 is 4 μH, the first and second capacitors 2 and 3 are compared with the capacitor 8 forming the resonance circuit. Since the capacitance of the second capacitors 2 and 3 is about 60 times, the influence of the first and second capacitors 2 and 3 on the resonance frequency can be ignored.

A primary winding of a transformer 7 is connected in parallel with the capacitor 8. A load is connected to a secondary winding of the transformer 7 via a rectifying and smoothing circuit 9, and a DC current is supplied to the load. . In general, the excitation impedance of the transformer 7 is relatively large. Therefore, the transformer 7 connected in parallel with the capacitor 8 can be regarded as an equivalent pure resistance component when viewed from the capacitor 8 side. . That is, when the load current increases, this corresponds to a case where the value of the pure resistance component decreases, and the Q of the resonance circuit including the reactor 6 and the capacitor 8 decreases. Conversely, if the load current decreases,
This corresponds to the case where the value of the pure resistance component increases, and the Q of the resonance circuit including the reactor 6 and the capacitor 8 increases. In any case, the effect on the resonance frequency can be ignored.

Therefore, a resonance circuit is formed by the reactor 6 and the capacitor 8 connected in series, and the resonance frequency is about 116 KHz in the case of the above-described circuit constants. In that case
1, The switching frequency for controlling the ON / OFF of the second switching elements 4 and 5 is set to be higher than this resonance frequency.

FIG. 2 is an explanatory diagram of resonance characteristics. Assuming that a resonance frequency of a resonance circuit including the reactor 6 and the capacitor 8 is f ₀ ,
When the load is equal to or less than the rated load, the switching frequency for controlling on / off of the switching elements 4 and 5 is changed to the resonance frequency.
was higher for example, f ₁ than f _0, the closer to the rated load, is intended to approximate the switching frequency to the resonance frequency f _0. That is, since the switching frequency is set to the resonance frequency f ₀ , the circuit constant may be set based on the resonance frequency f ₀ , and the circuit components can be reduced in size.

Fig. 3 shows an example of a MOS FET (MOS
21 is an explanatory diagram of a field-effect transistor), 21 is a source electrode, 22 is a drain electrode, 23 is a gate electrode, 24 is a gate insulating film, and 25 is a parasitic diode. The source electrode 21 is connected to the upper contact region N ⁺ , and the drain electrode 22 is connected to the lower contact region N ⁺ . An oxide film is usually used for the gate insulating film 24.

By applying a gate voltage to the gate electrode 23, P
An inversion layer is generated in the region, the source electrode 21 → N ⁺ region → P region → N ^- current flows through a path region → N ⁺ region → drain electrode 22, and controls on the current, the off by gate voltage that Can be. A parasitic diode 25 indicated by a dotted line is formed between the P region and the N ⁻ region. This parasitic diode 25
Are indicated by reference numerals 15 and 16 in FIG. Also, a parasitic capacitance between the source electrode 21 and the drain electrode 22 is formed.

Thousands or tens of thousands of such vertical FET basic cells are formed on one chip to constitute a power MOS FET.

The control circuit 10 compares whether or not the output DC voltage from the rectifying / smoothing circuit 9 is a set value, and controls the switching frequency of the first and second switching elements 4 and 5 according to an error with respect to the set value. When the first switching element 4 is turned on, the rectified output voltage of the full-wave rectifier circuit 1 is applied to the primary winding of the transformer 7 via the capacitor 3 and the reactor 6, and the second switching element 5 is turned on. , The transformer 7 via the capacitor 2 and the reactor 6
, And an alternating voltage is applied to the primary winding. As a result, a voltage is induced in the secondary winding of the transformer 7, and the voltage is rectified and smoothed by the rectifying / smoothing circuit 9 to become an output DC voltage, which is supplied to a load (not shown).

The first and second capacitors 2 and 3 do not smooth the rectified output of the full-wave rectifier circuit 1 but function to block DC current, and act to flow the resonance current by the resonance circuit. Therefore, a large ripple current does not flow unlike the capacitor input type. Therefore, the power factor can be improved. Further, by switching at the resonance frequency or a frequency close to the resonance frequency, the switching loss in the switching elements 4 and 5 can be reduced to a negligible level, so that it is easy to increase the frequency.

FIG. 4 is a diagram for explaining the operation of the embodiment of the present invention.
Represents the source-drain voltage of the first switching element 4, and (b) represents the source-drain voltage of the second switching element 5. In the ON state, the source-drain voltage becomes zero. (C) and (d) show currents flowing through the first and second switching elements 4 and 5, and (e) shows a resonance current by a resonance circuit including the reactor 6 and the capacitor 8.

By setting the switching frequency higher than the resonance frequency, the current flowing through the switching elements 4 and 5 becomes a lag current when viewed from the switching elements 4 and 5 side. Since this delay current flows through the parasitic diodes 15 and 16 of the switching elements 4 and 5, the current becomes a negative current as shown in (c) and (d). That is, when the first switching element 4 is turned on as shown in (a), as shown in (c), after a delay current flows in the reverse direction via the parasitic diode 15, a part of the resonance current is reduced. Flows forward.

FIG. 5 is an explanatory diagram of voltage and current according to the embodiment of the present invention. FIG.
5 shows a voltage V1 (solid line) and a current I1 (dotted line). (B) shows the voltage V2 (solid line) and current I2 (dotted line) of the switching elements 4 and 5 when the load current is large. That is, when the load current is small, the switching frequency is high, and when the load current is large, the switching frequency is low, and switching can be performed at a point where the current I2 becomes zero. Therefore, when the load current increases, the switching loss can be reduced to a negligible level.

(C) is a rectified output voltage V3 by the full-wave rectifier circuit 1,
(D) shows the current I3. If the switching elements 4 and 5 are turned on and off at the cycle of the rectified output voltage V3, the current I3 shown in (d) flows. That is, a large ripple current for charging the capacitor does not flow through the full-wave rectifier circuit 1 but becomes a current that flows over the engine in almost a half cycle. As a result, the AC power supply I4 shown in (f) flows with respect to the AC voltage V4 shown in (e). That is, although the current I4 has a distorted waveform, the conduction angle increases, so that the peak value of the current I4 may be low. As a result, the fundamental wave component of the AC current I4 is increased, and the power factor can be improved, for example, it can be 90% or more.

The present invention is not limited to the above-described embodiment, but can be variously added and changed.

〔The invention's effect〕

As described above, the present invention provides a transformer via the reactor 6 between the connection point of the first and second capacitors 2 and 3 and the connection point of the first and second switching elements 4 and 5. 7 and a capacitor 8 is connected in parallel with the primary winding to form a resonance circuit including the reactor 6 and the capacitor 8.
2, 3 act to flow the resonance current and do not smooth out the full-wave rectified output unlike the capacitor input type, so that the charging current with a large peak value does not flow, thereby reducing the power factor. Can be greatly improved.

Further, as the load current increases, the switching can be performed at a point where the voltage or the current is zero as the switching frequency closer to the resonance frequency of the resonance circuit. Therefore, the switching loss can be reduced to a negligible level. Accordingly, it is possible to easily increase the switching frequency.

[Brief description of the drawings]

FIG. 1 is a main part circuit diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of resonance characteristics, FIG. 3 is an explanatory diagram of a MOS FET, FIG. 4 is an operational explanatory diagram of an embodiment of the present invention, FIG. FIG. 6 is an explanatory diagram of voltage and current according to the embodiment of the present invention. FIG.
The figure is an explanatory view of the voltage and the current of the conventional example. 1 is a full-wave rectifier circuit, 2 and 3 are first and second capacitors, 4 and 5 are first and second switching elements, 6 is a reactor, 7 is a transformer, 8 is a capacitor, 9 is a rectifying and smoothing circuit, 10 is a control circuit, and 11 is an AC power supply.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshihisa Kaji 237 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Minoru Nakano 237-Sakado, Takatsu-ku, Kawasaki City, Kanagawa Prefecture Incorporated company (56) References JP-A-1-264564 (JP, A) JP-A-58-87486 (JP, U) JP-B-62-36470 (JP, B2)

Claims (1)

(57) [Claims] 1. A full-wave rectifier circuit for rectifying an AC voltage.
And the first and second capacitors (2, 3) connected in series for applying the rectified output voltage of the full-wave rectifier circuit (1) and the first and second capacitors (2, 3) connected in series.
A second switching element (4, 5); a connection point between the series-connected first and second capacitors (2, 3); and a series-connected first and second switching element (4, 5).
5), the first and second capacitors (2,
A resonance circuit in which a capacitor (8) and a reactor (6) having a smaller capacity than the capacitance of 3) are connected in series, and a transformer (1) having a primary winding connected in parallel with the capacitor (8) of the resonance circuit. 7), a rectifying and smoothing circuit (9) connected to the secondary winding of the transformer (7), and alternately turning on and off the first and second switching elements (4, 5) connected in series. Setting a switching frequency higher than a resonance frequency of the resonance circuit, controlling the switching frequency in accordance with a load;
And a control circuit (10) for stabilizing the output DC voltage of the resonance type.