DC power supply device with constant power output level

Details DC power supply device with constant power output level DC power supply device with constant power output level

2002-03-27

2004-06-15

Sherry, Michael (Department: 2838)

Electric power conversion systems

Current conversion

Having plural converters for single conversion

C363S067000

Reexamination Certificate

active

06751107

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relate to a switching power supply device. More particularly, it relates to a DC power supply device with a constant power output level and output power control of such a device.
2. Description of the Related Art
FIG. 19
of the accompanying drawings is a schematic circuit diagram of a switching power supply device to be typically used for a film forming device. In
FIG. 19
, reference symbols Q
1
through Q
4
denote respectively switching elements, which form a full-bridge; and reference symbol T
1
denotes a transformer, while D
1
through D
4
respectively denotes rectifier diodes for the output of the transformer; and L denotes an output choke coil. Additionally, reference symbols Co, R, Vin, n
1
, n
2
and VQ respectively denote a smoothing capacitor, a load, an input voltage source, a primary winding, a secondary winding and output voltage.
Constant power control is required for controlling a film forming device. Therefore, the power supply device of the system operates for power output in a manner as illustrated in FIG.
21
. In
FIG. 21
, Vo denotes the output voltage of the power supply device and Io denotes the output current of the device.
In
FIG. 21
, V
1
and I
2
respectively indicate the highest output voltage and the largest output current, while V
2
and I
2
respectively indicate the output voltage and the output current at the opposite ends of the power output performance curve of the device. The constant power output range is found between A and B in FIG.
21
. If V
1
=500V and I
2
=40A in
FIG. 21
, the output capacity of the power supply device is 20 kW (V
1
×I
2
). However, the maximum output of the device may be 10 kw if I
1
=20A and V
2
=250V for I
C
×V
1
(=l
2
×V
2
) because of constant power control.
Therefore, the transformer is poorly exploited as it is used at the output level of 10 kW although it has a capacity of 20 kW. On the other hand, the switching elements Q
1
through Q
4
are arranged to form a full-bridge and used for pulse width control (PWM) with a constant cycle period Ts (FIG.
20
). PWM itself is well known. FIGS.
20
(
a
) through
20
(
d
) show the waveforms of gate signals of Q
1
through Q
4
; and FIG.
20
(
e
) shows the waveform of the pulse output of the full-bridge (the primary input of the transformer) that has a pulse width of t. Because of constant power output, the output voltage is reduced to consequently show a small pulse width when the output current of the power supply device shows the maximum level. This means that a large smoothing filter is needed to rectify and smooth the voltage (see waveform FIG.
20
(
f
)).
As pointed out above, the conventional control method is accompanied by disadvantages including that the transformer is poorly exploited and hence the use of a large filter is required and that the effective current of the switching/transforming section and that of the primary winding of the output transformer are increased to increase the loss of the output transformer and that of the switching elements because of the small pulse width in constant power output operations, which requires the use of large heat sink fins to obstruct efforts for down-sizing.
SUMMARY OF THE INVENTION
In view of the drawbacks of the prior art, it is therefore an object of the present invention to provide a power supply device that can fully exploit its transformer and minimize the factors that give rise to ripples in the output voltage so that the transformer and the smoothing filter may be downsized and the loss of power of the switching elements may be reduced in constant power output operations. Thus, a power supply device according to the invention can be provided with reduced dimensions.
The first aspect of the invention, a power supply device supplying an output voltage from smoothing circuits to a load, comprising; a first primary winding and a second primary winding, and a first secondary winding and a second secondary winding magnetically coupled respectively to said first and second primary windings; a first current supply circuit and a second current supply circuit for respectively supplying electric currents to said first and second primary windings and inducing alternating voltages in said first and second secondary windings by making said electric current flow to said first and second primary windings; a rectifying circuit for rectifying the respective alternating voltages induced in said first and second secondary windings and being connected to said first and second secondary windings respectively at their ends; and a smoothing circuit for smoothing the voltage output from said rectifying circuit, other ends of said first and second secondary windings being short circuited, said first and second current supply circuits being adapted to control phases of alternating currents supplied to said first and second primary windings respectively.
The second aspect of the invention is directed to the power supply device according to the first aspect, wherein an operation period of said power supply device includes a period where said first and second secondary windings are connected in parallel relative to said rectifying circuit as a function of polarities of the voltages induced in said first and second secondary windings respectively, and said period of said parallel connection is changed by controlling said phases by means of said first and second current supply circuits.
The third aspect of the invention is directed to the power supply device according to the second aspect, wherein an operation period of said power supply device includes a period where said first and second secondary windings are connected in series relative to said rectifying circuit for a period as a function of polarities of the voltages induced in said first and second secondary windings respectively, and said period of said series connection is changed by controlling said phases by means of said first and second current supply circuits.
The fourth aspect of the invention is directed to the power supply device according to the second aspect, further comprising a measuring circuit for measuring an output voltage and output current supplied to said load and controlling phases of said first and second current supply circuits based on a measurement result.
The fifth aspect of the invention is directed to the power supply device according to the third aspect, further comprising a measuring circuit for measuring the output voltage and output current supplied to said load and controlling phases of said first and second current supply circuits based on the measurement results.
The sixth aspect of the invention is directed to the power supply device according to the fourth aspect, wherein said measuring circuit prolongs the period of connecting said first and second secondary windings in parallel by controlling said phases of said first and second current supply circuits upon detecting any increase exceeding a predetermined upper limit in said output current, and shortens the period of connecting said first and second secondary windings in parallel by controlling said phases of said first and second current supply circuits upon detecting any decrease from said upper limit in said output current.
The seventh aspect of the invention is directed to the power supply device according to the fifth aspect, wherein
said measuring circuit prolongs the period of connecting said first and second secondary windings in parallel by controlling said phases of said first and second current supply circuits upon detecting any increase exceeding a predetermined upper limit in said output current, and shortens the period of connecting said first and second secondary windings in parallel by controlling said phases of said first and second current supply circuits upon detecting any decrease from said upper limit in said output current.
The eighth aspect of the present invention is directed to the power supply device according to the fifth aspect, wherei

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