JPH02311165A - Pulse width control current resonance converter - Google Patents

Abstract

PURPOSE:To prevent mutual interference between a plurality of converters during parallel operation by varying the current to be fed to a DC overlapping coil according to the variation of output voltage thereby varying the inductance of a resonance coil and controlling the output voltage. CONSTITUTION:A permanent magnet is arranged in the gap of the core of a resonance coil while furthermore a DC overlapping coil is provided, then the current flowing through the coil is controlled variably thus controlling the resonance frequency variably. When the output voltage from a smoothing circuit increases or decreases, the voltage error is amplified through an error amplifier 17 then the amplified output voltage is converted through a voltage/ current converter 16 into current which is fed to a coil 15. When the resonance frequency is increased or decreased by increasing or decreasing the inductance of a coil 8, output voltage is regulated automatically and reset to a predetermined level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pulse width controlled current resonant converter.

[Conventional technology]

Conventional current resonant converters control output voltage using a frequency control method. In other words, a sinusoidal half-wave current is obtained by switching a DC power supply to a resonant circuit consisting of a coil and a capacitor, but the length of time that the switching is on is a constant value determined by the resonant frequency of the resonant circuit. By controlling the length of time that the switching is in the off state, the duty ratio, that is, the ratio of the on time to the switching period, is changed to variably control the output voltage.

[Problem to be solved by the invention]

In the conventional current resonant converter described above, the resonant frequency of the resonant circuit is a constant value, and the switching duty ratio must be changed in order to variably control the output voltage, and when multiple units are operated in parallel, each There is a problem in that the switching periods become irregular and the combined output voltage changes in a beat-like manner and becomes unstable.

[Means to solve the problem]

The converter of the present invention includes a resonant circuit in which a first coil wound around a magnetic core with a permanent magnet interposed therebetween and a capacitor are connected in series, and a connection between the resonant circuit and a DC power source is turned on at preset intervals. a switch circuit that switches the connection to an OFF state when the current flowing through the resonant circuit returns to zero in response to this, a smoothing circuit that smoothes and outputs the voltage across the capacitor, and an output of the smoothing circuit. It includes a control circuit that generates a control signal indicating the magnitude of voltage, and a second coil that is wound around the magnetic core and that varies the inductance value of the first coil in response to the control signal.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

An input capacitor 5 is connected between input terminals 1 and 2,
Coil 8 and capacitor 9 via switching circuit 6
A resonant circuit consisting of is connected. The capacitor 9 has a flywheel diode connected in parallel, and both ends of the capacitor 9 are connected to the output terminals 3 and 4 via a smoothing circuit composed of a coil 10 and a capacitor 11.

As shown in FIG. 2, the resonance coil 8 is wound around a magnetic core 18 with a permanent magnet 19 installed in the gap, and a DC superimposition coil 15 is further wound around the magnetic core 18. The magnetization characteristic of the magnetic core 18 is non-linear as shown in FIG. 4, and is biased by a magnetizing force H by the permanent magnet 19. By changing the direction and magnitude of the direct current in the coil 15, the bias point can be moved above and below the magnetizing force H, and the inductance value of the coil 8 can be changed.

As shown in FIG. 3, the control circuit 13 of the switch circuit 6 raises the gate voltage of the switching transistor 14 at preset intervals T (time tn), and turns off the source and drain of the transistor 14. Switch to state. In response, a sinusoidal resonant current flows through the coil 8. The current detector 12 detects the timing at which this resonant current returns to zero and causes the output voltage of the control circuit 13 to fall (time tr or trz), when the resonant frequency of the resonant circuit is high. As shown by the solid line in FIG. 3, a waveform with a low duty ratio is obtained, and conversely, when the resonance frequency is low, a waveform with a high duty ratio is obtained as shown by the broken line in FIG.

The output voltage of the smoothing circuit changes up or down depending on the level of the duty ratio.

When the output voltage of the smoothing circuit rises (or falls) from the desired value, the error voltage is amplified by the error amplifier 17, and the amplified output voltage is converted into a current by the voltage-current converter 16 and supplied to the coil 15. and reduce the inductance of coil 8 (
By increasing (or increasing) the resonant frequency, the output voltage is automatically adjusted to decrease (or increase), and the output voltage is returned to the desired value.

In this way, a permanent magnet is provided in the gap between the magnetic cores of the resonant coil, and a DC superimposition coil is also provided to variably control the current flowing through this, thereby variably controlling the resonant frequency. The switching duty ratio can be varied while keeping the cycle constant, and pulse width control type operation can be realized. Therefore, even if multiple units are operated in parallel, the output voltage will not become unstable as in the conventional circuit.

〔Effect of the invention〕

As explained above, the present invention enables pulse width control with a constant frequency by changing the current applied to the DC superimposing coil according to changes in the output voltage, changing the inductance of the resonant coil, and controlling the output voltage. This has the effect of preventing mutual interference when multiple converters are operated in parallel. Furthermore, since DC magnetization is applied using a permanent magnet, the power required for control using DC superimposed current can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a top view illustrating a resonant coil in an embodiment of the present invention, and Fig. 3 is an operation of the embodiment of the present invention. FIG. 4 is a characteristic diagram showing the magnetization characteristics of the magnetic core of the resonant coil according to the embodiment of the present invention.

1.2...Input terminal, 3,4...Output terminal, 5,9
゜11... Capacitor, 6... Switch circuit, 7.
...Diode, 8.10.15...Coil, 12.
...Current detector, 13...Control circuit, 14...Transistor, 16...Voltage-current conversion circuit, 17...
Error amplifier, 18...Magnetic core, 19...Permanent magnet.

Claims (1)

[Claims] A resonant circuit in which a first coil wound around a magnetic core with a permanent magnet interposed therebetween and a capacitor are connected in series, and a connection between the resonant circuit and a DC power source are turned on at preset intervals in response to the resonant circuit. a switch circuit that turns off the connection when the current flowing through the resonant circuit returns to zero; a smoothing circuit that smoothes and outputs the voltage across the capacitor; and a control that indicates the magnitude of the output voltage of the smoothing circuit. A pulse width control method comprising: a control circuit that generates a signal; and a second coil that is wound around the magnetic core and that varies the inductance value of the first coil in response to the control signal. Current resonant converter.