Dc-Dc power supply

Details Dc-Dc power supply Dc-Dc power supply

2003-03-07

2004-02-24

Han, Jessica (Department: 2838)

Electric power conversion systems

Current conversion

Including an a.c.-d.c.-a.c. converter

C363S016000, C323S267000, C307S032000

Reexamination Certificate

active

06697268

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a DC-DC power source device for obtaining a prescribed DC power from DC power source.
BACKGROUND ART
FIG. 6
shows the configuration of an AC variable speed device with a conventional built-in DC-DC power source device. In
FIG. 6
, reference numeral
30
a
designates a three-phase AC power source;
31
a
, a converter unit which converts AC power to DC power;
32
, a neutral point between electrode terminals P and N of a DC main circuit power source;
33
, a P side smoothing circuit connected between the anode P and the neutral point
32
of the DC main circuit power source; and
34
, an N side smoothing circuit connected between the cathode N and the neutral point
32
of the DC main circuit power source. Reference numeral
35
denotes a P side balancing circuit connected between the anode terminal P and the neutral point
32
of the DC main circuit power source;
36
, an N side balancing circuit connected between the cathode terminal N and the neutral point
32
of the DC main circuit power source.
In addition, reference numeral
37
a
denotes an inverter unit that inverts DC power of the DC main circuit power source to AC power with a variable frequency and a variable voltage;
38
a
, an induction motor driven at a variable speed;
39
a
, a load circuit comprising the inverter unit
37
a
and the induction motor
38
a
and operates as a load of the DC main circuit power source.
Further, reference numeral
40
indicates a starting circuit connected between the anode terminal P of the DC main circuit power source and a switching control circuit
45
;
41
, a high-frequency transformer having two secondary windings;
42
, a rectifier circuit diodes for generating a DC output current from the high-frequency transformer
41
; and
43
,a rectifier circuit capacitor.
Reference numeral
44
designates a DC rectifier circuit comprising the rectifier circuit diodes
42
and the rectifier circuit capacitor
43
;
45
, a switch control circuit;
46
,a switching circuit;
47
, a secondary rectifier circuit diode;
48
, a secondary rectifier circuit capacitor;
49
, a secondary load such as a control unit (not shown) for controlling the inverter unit
37
a.
The DC-DC power source device contained in the conventional AC variable speed device is comprised of the starting circuit
40
, the high frequency transformer
41
, the DC rectifier circuit
44
, the switch control circuit
45
, the switching circuit
46
, the secondary rectifier circuit diode
47
and the secondary rectifier circuit capacitor
48
.
The operation of the conventional AC variable speed device is set forth below. AC power of the three phase AC power source
30
a
is converted to DC power by the converter unit
31
a
and the converted DC power is then filtered by a smoothing circuit (the P side smoothing circuit
33
and the N side smoothing circuit
34
) to work as the DC main circuit power source. The inverter unit
37
a
inverts DC power of the DC main circuit power source to AC power with variable frequency and variable voltage, thereby driving the induction motor
38
a
at variable speeds.
The conventional AC variable speed device contains the DC-DC power source device as DC power source of control unit (not shown) for controlling the inverter unit
37
a
, supplying a prescribed DC power source to the control unit by utilizing the DC main circuit power source. Here, the P side balancing circuit
35
and the N side balancing circuit
36
are used to regulate a voltage sharing ratio between the P side smoothing circuit
33
and the N side smoothing circuit
34
to lower the voltage applied to these smoothing circuits
33
and
34
below their withstand voltage.
It is assumed that these balancing circuits (P side balancing circuit
35
and N side balancing circuit
36
) do not exist. Defining that an internal impedance of the P side smoothing circuit
33
is r
1
, an internal impedance of the N side smoothing circuit
34
is r
2
, a voltage applied to the P side smoothing circuit
33
is v
1
, a voltage applied to the N side smoothing circuit
34
is v
2
, and a DC main circuit voltage smoothed is V DC
1
, the voltage v
1
applied to the P side smoothing circuit
33
and the voltage v
2
applied to the N side smoothing circuit
34
are expressed by the following formulas (1) and (2), respectively:
v
1
=(
r
1
/(
r
1
+
r
2
))×
V
DC1
  (1)
v
2
=(
r
2
/(
r
1
+
r
2
))×
V
DC1
  (2)
When the capacitance and withstand voltage V of the P side smoothing circuit
33
are identical with those of the N side smoothing circuit
34
, and when the internal impedance r
1
of the P side smoothing circuit
33
are 3 times larger than the internal impedance r
2
of the N side smoothing circuit
34
, the formulas (1) and (2) are expressed by following formulas (3) and (4), respectively:
v
1
=(¾)×
V
DC1
  (3)
v
2
=(¼)×
V
DC1
  (4)
Therefore, the withstand voltage V of the P side smoothing circuit
33
must be at least ¾ times larger than that of the DC main circuit voltage V
DC1
. The balancing circuits (P side balancing circuit
35
and N side balancing circuit
36
) are disposed in order to adjust the difference in voltage applied to the smoothing circuits, caused by the difference between the internal impedance r
1
of the P side smoothing circuit
33
and the internal impedance r
2
of the N side smoothing circuit
34
.
Given now that, the impedance of the P side balancing circuit
35
is R
21
, the impedance of the N side balancing circuit
36
is R
22
, the combined resistance of the impedance R
21
of the P side balancing circuit
35
and the internal impedance r
1
of the P side smoothing circuit
33
is Rc
21
, and the combined resistance of the impedance R
22
of the N side balancing circuit
36
and the internal impedance r
2
of the N side smoothing circuit
34
is Rc
22
, the voltage v
1
applied to the P side smoothing circuit.
33
and the voltage v
2
applied to the N side smoothing circuit
34
are expressed by the following formulas (5) and (6),respectively:
v
1
=(
Rc
21
/(
Rc
21
+
Rc
22
))×V
DC1
  (5)
v
2
=(
Rc
22
/(
Rc
21+
Rc
22
))×V
DC1
  (6)
When the impedance R
21
of the P side balancing circuit
35
is assumed as R
21
<<r
1
, and when the impedance R
22
of the N side balancing circuit
36
is assumed as R
22
<<r
2
, the combined resistances Rc
21
and Rc
22
are expressed as Rc
21
≈R
21
and Rc
22
≈R
22
, respectively.
Assuming herein that R
21
=R
22
, the formulas (5) and (6) can be expressed by the following formulas (7) and (8), respectively.
v
1
=
V
DC1
/2  (7)
v
2
=
V
DC1
/2  (8)
The voltage v
1
applied to the P side smoothing circuit
33
and the voltage v
2
applied to the N side smoothing circuit
34
are ½ times larger than DC main circuit voltage V
DC1
, thereby making it possible to adjust the imbalance voltage applied to each smoothing circuit.
Therefore, the withstand voltages v of the P side smoothing circuit
33
and the N side smoothing circuit
34
are lowered to equal to or less than ½ of the DC main circuit voltage V
DC1
.
An operation of the DC-DC power source device contained in the conventional AC variable speed device will be described. Application of AC power source
30
a
to the AC variable speed device causes the DC main circuit power constituted by the converter unit
31
a
and the smoothing circuit (P side smoothing circuit
33
and N
1
side smoothing circuit
34
) to charge the rectifier circuit capacitor
43
through the starting circuit
40
. Besides, the rectifier circuit capacitor
43
supplies the charged DC power to the switch control circuit
45
, and as a result, the circuit
45
outputs a high frequency oscillating signal to the switching circuit
46
. The switching circuit
46
oscillates at high frequency and supplies high frequency power to the high frequency transformer
41
.

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