Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-02-26
2003-01-07
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S016000
Reexamination Certificate
active
06504732
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a non-contact electrical power transmission system which includes a transformer with separable primary and secondary windings. The system transmits electric power from the primary side to the secondary side of the transformer in a condition in which a core wrapped with a primary winding and a core wrapped with a secondary winding remain out of contact with each other.
Heretofore, in many places, a non-contact electrical power transmission system has been commercially applied. Such systems configure a transformer in which the primary winding and the secondary winding are separable from each other with a core wrapped with a primary winding and a core wrapped with a secondary winding. The system transmits power from the primary side to the secondary side by electromagnetic induction with the primary core and the secondary core remaining out of contact with each other.
However, in most conventional non-contact electrical power transmission systems, a load connected between output terminals at the secondary side of a transformer has been specified. There has not been discovered a commercially applied example of a non-contact electrical power transmission system which is applicable to plural kinds of loads as a load connectable between output terminals, and also even to a kind of load whose current changes over a wide range.
Meanwhile, such non-contact electrical power transmission systems transmit an electric power from the primary side to the secondary side with an electrical insulator between the primary side of the above-mentioned transformer as electric power supply side and the secondary side having a load connected between output terminals. The degree of magnetic coupling of transformer is low, the magnetic flux interlinked to the secondary winding is fewer than that generated in the primary winding, and a leakage inductance develops due to leakage magnetic flux.
Although the frequency of a high-frequency AC voltage supplied to the primary winding of such transformers is generally in the audible-range frequency or above (about 20 kHz or more), the above-mentioned separable transformer is low in the degree of magnetic coupling and has a leakage inductance, whereby the induced voltage in the secondary winding is reduced and a voltage drop in induction reactance due to leakage inductance develops. As a result, the voltage supplied to a load may be smaller than a desired load voltage, or the current flowing to a load may be smaller than a desired load current. Explaining with a specific example, where various plural kinds of devices with a constant load voltage and variable load current are applicable to a load, the larger the load current of a load, the lower the voltage across the load becomes, whereby the performance inherent in devices cannot be exhibited.
Referring to FIG.
39
(A), a prior-art rectifier circuit
7
is connected to the secondary side of a separable transformer T. A circuit for supplying a load current I to a load
10
consists of a variable resistance in series with a choke coil LCH. A high-frequency AC voltage is applied by an inverter
3
to the primary side of the transformer T. A secondary winding n
2
of the transformer T includes a center tap
5
e
. One terminal of the load
10
is connected to the center tap
5
e
. The ends of the secondary winding n
2
are connected to the anodes of diodes D
2
and D
3
. The cathodes of the diodes D
2
and D
3
are connected together, and their junction is connected to the choke coil LCH. A capacitor C
3
is connected in parallel with the load
10
.
In the circuit shown in FIG.
39
(A), a high-frequency square-wave AC voltage, having a maximum amplitude 70 volts and a frequency of about 97 kHz as shown in FIG.
39
(B) is applied to a primary winding n
1
of the transformer T. With the inductance value of the choke coil LCH taken as 100 &mgr;H, the capacitance of the capacitor C
3
connected parallel to the load
10
taken as
100
&mgr;F, a gap g between a primary core
5
c
of the transformer T and a secondary core
5
d
taken as 2 mm, measuring a load voltage (output voltage)/load current characteristics and a load power/load current characteristics by changing variously the resistance value of the load
10
causes characteristics to be obtained as shown in FIG.
41
. In
FIG. 41
, the axis of abscissa is for a load current
1
, the axis of ordinate on the left side for a load voltage V
0
, and the axis of the ordinate on the right side for a load power P, the curve V indicating the load voltage and the curve P indicating the load power.
The transformer T has a configuration as shown in
FIG. 40
, in which the primary winding n
1
is separately wrapped at two leg portions of the U-type primary core
5
c
, the secondary winding n
2
is separately wrapped at two leg portions of the U-type secondary core
5
d
, and the center tap
5
e
is provided at the middle point of the secondary winding n
2
. Now, the inductance value when viewed from the primary. winding terminals A-A′ of the transformer T is 112 &mgr;H, the inductance value when viewed from the secondary winding terminals B-B′ is 42 &mgr;H, and the mutual inductance value between the primary winding n
1
and the secondary winding n
2
is 91 &mgr;H.
It will be understood from
FIG. 41
that as the load current I increases, the load voltage V
0
substantially decreases monotonously, while the load power P becomes smaller in increased values (becomes saturated) as the load current I becomes larger. In a non-contact electrical power transmission system for charging load
10
, a matching capacitor is connected in parallel or series with the secondary winding n
2
of the transformer T in order to offset an effect due to the leakage inductance of the transformer T, thereby increasing an effective power taken from the primary side to secondary side of the transformer T (improving a power factor by load matching). Providing such a matching capacitor causes a power transmission efficiency to be significantly improved for a certain load, thereby allowing the system to be miniaturized. Therefore, the matching capacitor is an important component in commercially applying a non-contact electrical power transmission system.
However, in a non-contact electrical power transmission system provided with the above-mentioned matching capacitor, a problem exits in that for a load whose load current I varies largely, the load voltage V
0
lowers remarkably compared with a case where no matching capacitor is provided. For example, in a system which has substantially the same circuit configuration as shown in the above-mentioned FIG.
39
(A) and in which the secondary winding n
2
of the separable transformer T is connected in parallel with a matching capacitor C
2
as shown in FIG.
42
(A), supplying a high-frequency AC voltage of the square-wave shape having a maximum amplitude 70 volt and a frequency of about 97 kHz as shown in FIG.
42
(B) to the primary winding n
1
of the transformer T and changing variously the resistance value of the load
10
consisting of a variable resistance causes a load voltage/load current characteristics and a load power/load current characteristics as shown in
FIG. 44
to be obtained. Now, in
FIG. 44
, the axis of abscissa is for the load current I, the axis of ordinate on the left side for the load voltage V
0
, and the axis of the ordinate on the right side for the load power P, the curve V indicating the load voltage and the curve P indicating the load power. Hereinafter, a value obtained with (varying range of load voltage V
0
)/(varying range of load current) is referred to as the voltage change rate.
It will be understood from
FIG. 44
that the more the load current I increases, the more the voltage change rate of the load voltage V
0
becomes large. It will be also understood that as load current I increases, the load power P exhibits a characteristics having a peak at a certain load current value. Furthermore, it will be understood that in a load current region for a ver
Darby & Darby
Matsushita Electric & Works Ltd.
Patel Rajnikant B.
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