JPS61258671A - Series resonance converter - Google Patents

Abstract

PURPOSE:To narrow the varying range of an operating frequency for a variation in a load current by connecting in series a parallel resonator with the AC side terminal of a rectifier. CONSTITUTION:Semiconductor switches 11, 18 are complementarily turned ON and OFF to flow a DC resonance current i1 from DC power sources 12, 19 through a rectifier 13 to a load 14. In this case, a parallel resonator 23 is formed of an inductor 24 and a capacitor 23, and connected in series with a series resonator 26 of a capacitor 16 and an inductor 17. The resonance frequency fs of the resonator 23 is set to a lower value than the resonance frequency f0 of the resonator 26 as the lowest operating frequency of a converter. Thus, when the operating frequency approaches the frequency fs, the impedance of the resonator 23 abruptly increases. Accordingly, the current i1 is abruptly decreased to control an output voltage.

Description

[Detailed description of the invention] "Industrial application field" This invention includes a series resonant circuit, a rectifier circuit and a semiconductor switch connected in series, converts DC power into DC power, and supplies the DC power to a load. Regarding series resonant converters.

"Prior Art" A series resonant converter is composed of a series resonant circuit of an inductor and a capacitor, a rectifier circuit connected in series with the series resonant circuit, and a semiconductor switch such as a bipolar transistor (or MOS transistor) or a diode. Ru. The resonant current flowing through the semiconductor switch naturally extinguishes, and there is no need to forcibly turn off the semiconductor switch, so there is no switching loss in principle, and therefore it is easy to increase the frequency, making the device noiseless. The effect of compactness and weight reduction can be expected. Furthermore, since the output characteristics are essentially constant current characteristics, the device can be easily protected even if an overload or load short circuit occurs.

Figure 3 shows a conventional series resonant converter (e.g. W8
Me MurraY -'l'he thyristo
r electronic transformer a
power converter using a
high-frequency 1ink,
IEEE Trans on IGA, NO4.

p451). FIG. 4 shows operating waveforms of each part in FIG. 3.

When the semiconductor switch 11 is turned on in FIG.
6-A series resonant current 's (solid line) flowing through the inductor 17 and returning to the DC power supply 12 as shown in FIG. 4A. Inductance of inductor 17 is 10, capacitor 16
If the capacitance of C11% capacitor 15 is -14tC@t, then C, t>>C, so i8 is πC Q-after t: 4th from the beginning of flow.
As shown in Figure A, the voltage of the capacitor 16 becomes zero, and the voltage of the capacitor 16 at that time is the output voltage (voltage of the load 14) vo and the DC type @12
If the voltage is larger than the sum of the voltage of
A current 11 flows through the lead 21 as shown by the dotted line. This resonant current i: is also a series resonant current between the inductor 17 and the capacitor 16, and its half period is πf stone]7. Along with this, the capacitor ν1 for the filter is passed through the rectifier circuit 13.
5:: A current i flows as shown in FIG. 4B.

Next, when the semiconductor switch 18 is turned on, as shown in FIG.
Capacitor voltage 15) - Rectifier circuit 13 - Semiconductor switch 18
The current i8 flows through the diode 22 and returns to the DC power supply 19, and once it becomes zero, the current i8 flows through the diode 22. These currents become a current i that charges the filter capacitor 15 through the rectifier circuit i3, and supply a DC voltage to the load 14.

-~ As mentioned above, since the current flowing through the semiconductor switches 11.18 is a series resonance current, these semiconductor switches f11.
18 becomes zero after the time πs/17s 5- after it is turned on, so there is no need to forcibly cut off the current flowing through these semiconductor switches 11 and 18, and therefore there is essentially no switching loss. High frequency operation is possible.

By the way, in this conventional converter, the rectifier circuit 13
The amount of charge transferred to the load side through the capacitor 16 can be calculated from the voltage change of the capacitor 16. In the steady state, the voltage waveform shown in Figure 4C is considered to be V, , = V,; therefore, the moving charge I Qo per half cycle is QO = CG ((V11+
V1! )+(Vtx-Vtx))=2CeV1g・
・・・・・・・・・・・・・・・(1). Here V
ll is the voltage of the capacitor 16 before the resonance current flows, v
ll is the voltage of the capacitor 16 before the next resonant current flows, and vll is the peak voltage of the capacitor 16. Letting f be the operating frequency, that is, the frequency at which the semiconductor switches 11.18 are turned on alternately, the average value of the current i is 1. is I, = QO/1/2 f = 4 CoVl, f
......(2). In a steady state, the voltage across filter capacitor 15 is constant, so all current I8 is supplied to load 14. If the resistance value of the load 14 is R, the output voltage v0 is V0=R-1,=(4C,V,,f)-R-・-
...(3) "Problem to be solved by the invention" From equation (3), the control of DC voltage v0 is C0*V1! or by controlling either f. It is currently difficult to control C0 continuously.

In addition, in a steady state, vl flows through the transistors 11 and 18 and the diodes 21 and 22 in parallel with each other, so that the feedback current i: or i; flows, so it is clamped by the DC power source 12°19 and becomes E, which is the DC type I! It cannot be controlled without changing the voltage of A12.19. Therefore, voltage control to maintain V at a constant value is generally performed by controlling the operating frequency f.

As can be seen from equation (C), when the value of R increases, the value of f decreases, and f becomes an audible frequency, causing a problem in that noise is generated. In addition, the operating frequency changes with load changes, making it difficult to take measures against noise.

The purpose of this invention is to reduce the range of change in operating frequency when performing constant voltage control from no load to full load.
``Means for solving inter-axis points'' that can clamp the lowest operating frequency This invention uses a resonance capacitor ν in series with a series resonant circuit.
A parallel resonant circuit in which resonant inductors are connected in parallel is connected, the resonant frequency of the parallel resonant circuit is selected to be lower than that of the series resonant circuit, and the lower limit of the operating frequency of the series resonant converter is clamped to the resonant frequency of the parallel resonant circuit. In this way, with conventional series resonant converters, it was not possible to clamp the lower limit of the operating frequency for constant voltage control of the output voltage from no load to full load, but in this invention, it is possible to clamp the lower limit of the frequency. I can do it.

"Example" ! Figure J1 is a circuit diagram showing a first embodiment of the present invention. In this example, the parallel resonant circuit 23 is composed of an inductor 24 and a capacitor 25, and the parallel resonant circuit 23 is composed of a series resonant circuit 2 of a capacitor 16 and an inductor 17.
6 is connected in series. In the pond, the same reference numerals as in FIG. 3 indicate the same parts.

The inductance of the inductor 24 of the parallel resonant circuit 23 is expressed as No.3. If the capacitance of the capacitor 25 is Cs, then the resonance frequency of the parallel resonant circuit 23 is fs=V2/π/J
7 is the resonant frequency fo of the series resonant circuit 26 composed of the inductor 17 and the capacitor 16; V2/π/
V no. Set lower than C0, and let fs be the lowest operating frequency of the converter. The impedance of the series resonant circuit 26 reaches its maximum at the resonant frequency fs, and as the operating wave number becomes higher than f, the impedance rapidly decreases.

Now, in FIG. 1, when the semiconductor switch 11 is turned on,
From the DC power supply 12 to the semiconductor switch 11 - rectifier circuit 13 -
Load 14 (Cover νri 15) -Ill.

Current 50 flows through the loop of the flow path 13, the capacitor 16, the inductor 17, and the parallel resonant circuit 23, and power is supplied to the load 14. The period of the current 18 passing through the parallel resonant circuit 23 is the period of alternately turning on and off the semiconductor switches 11 and 18, ie, the operating period, and the magnitude changes depending on the impedance of the circuit and therefore the operating frequency. When the operating frequency is sufficiently higher than the resonant frequency of the parallel resonant circuit 23, the impedance of the parallel resonant circuit 23 is sufficiently low, so the period of the current 18 is approximately 1/2/π/ as in the conventional example shown in FIG. V-61--. When the operating frequency approaches the resonant frequency of the parallel resonant circuit 23, the parallel resonant circuit 23
11 decreases rapidly because the impedance of .

Next, when the semiconductor switch 18 is turned on, the DC power supply 19- is connected to the column resonant circuit 23-inductor 17-capacitor 16-rectifier circuit 13-load 14 (capacitor 15)-rectifier circuit 1
3-A resonant current l, flows through the semiconductor switch 18. Similarly to the above case, the value of the current i also changes depending on the operating frequency.

This completes one cycle of operation. Parallel resonant circuit 23
The impedance of is small when the operating frequency is far from the resonant frequency f, but increases rapidly as it approaches fs. Therefore, by slightly changing the operating frequency near fs, the resonant current 11, that is, the output voltage can be controlled.

FIG. 82 is a circuit diagram showing a second embodiment of the present invention, in which the present invention is applied to a series resonant converter using a transformer to isolate DC input and output. That is, the primary side 1 of the transformer 27 is connected in series with the series resonant circuit 26, and the secondary side of the transformer 27 is connected to the AC side terminal of the rectifier circuit 13.

Furthermore, a parallel resonant circuit 23 is connected in series with the primary side of the transformer 27.
Connect. That is, the series resonant circuit 23 and the rectifier circuit 13 are connected in series via the transformer 27.

The operation according to the second embodiment is the same as the operation according to the first embodiment 6 shown in FIG. 1, so a description thereof will be omitted. According to this second embodiment, the input side and the output side can be isolated,
The output voltage can be freely set by adjusting the turns ratio nL/ns of the transformer 27.

"Effects of the Invention" As explained above, in this invention, the parallel resonant circuit is connected in series with the AC side terminal of the rectifier circuit. It is possible to operate a resonant converter outside the audio range. Therefore, if this invention is applied to a converter using a semiconductor switch capable of high-frequency operation such as a bipolar transistor or MOS transistor, it will be possible to operate at a frequency above the audible range, and it will be possible to implement a large-capacity device with no noise. There are advantages that can be realized.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a first embodiment of the present invention, Fig. 2 is a diagram showing an embodiment of W12 of the invention, Fig. 3 is a circuit diagram showing a conventional series resonant converter, and Fig. 4 is a circuit diagram showing a conventional series resonant converter. is the third
FIG. 3 is a waveform chart showing the operation shown in FIG. 11.18: Semiconductor switch, 12.19: DC power supply,
13: Rectifier circuit, 14: Load, 15° 16.25: Capacitor, 17.24: Inductor, 21.22: Diode, 23: Parallel resonant circuit, 26: Series resonant circuit. Patent applicant Takuya Kusano, agent of Nippon Telegraph and Telephone Ajishiki Company, once twice

Claims (1)

[Claims] (1) A series resonant circuit consisting of a resonant capacitor and a resonant inductor is connected in series with the AC side terminal of a rectifier circuit, and a plurality of semiconductor switches are controlled to turn on and off in the series circuit of the series resonant circuit and the rectifier circuit. In a series resonant converter which obtains a DC voltage from the rectifier circuit by alternately passing a positive current and a negative current from a DC power supply, a parallel resonant circuit in which a resonant capacitor and a resonant inductor are connected in parallel is connected in series with the series resonant circuit. A series resonant converter connected to the converter, wherein the resonant frequency of the parallel resonant circuit is selected to be lower than the resonant frequency of the series resonant circuit.