Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2000-05-18
2001-11-20
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S127000
Reexamination Certificate
active
06320772
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a circuit which converts AC power into DC power, in particular, to a converter circuit with a high power factor which exercises control in order to reduce harmonic frequency components included in the input current by utilizing a pulse width modulation technology.
PRIOR ART
Conventionally, a power unit which has a function of controlling harmonic distortion of the power supply in order to improve the power factor comprises a boost converter circuit which exercises control so that the AC input current becomes a sine-wave shape. For example, as described in the Japanese unexamined patent publication S63 (1988)-224698, after rectifying the input voltage the input current is controlled by the boost converter circuit since a circuit configuration is simple, particularly, in a single phase input power supply. This prior art has a configuration as shown in FIG.
19
. That is to say, after rectifying the AC power supply
1
one time with the rectifier diode circuits
102
a
,
102
b
,
102
c
and
102
d
, a DC power supply is created by the boost converter circuit configured of a reactor
106
, a switching element
103
, a diode
104
and a smoothing capacitor
7
to be supplied to a load
8
.
FIG. 21
is a control block diagram of the control circuit
110
for controlling circuits in FIG.
19
. In
FIG. 21
, an error Verr is gained between set DC voltage Vdc* in the comparison means
37
and actual DC voltage Vdc gained from the resistances
9
a
and
9
b
in
FIG. 19
, which passes through the compensating filter
32
so that the rectified output |Vac| gained by the resistances
111
a
and
111
b
in
FIG. 19
is inputted to the multiplier
31
to gain set current information |Iac*|. This |Iac*| is compared with actual input current information |Iac| detected as the voltage between both ends of the resistance
113
in
FIG. 19
by the comparison means
38
, of which the error information |Iac err| is gained to be sent to the compensating filter
133
. In the compensating filter
133
a filter operation is carried out to stabilize the input current wave form control. The output of the compensating filter
133
is sent to the comparator to be compared with the output signal from the oscillator
35
which is converted into a pulse width modulation signal PWMout. The pulse width modulation signal PWMout passes through the gate driving circuit
105
to drive and control the switching element
103
in FIG.
19
.
FIG. 20
shows a circuit where the number of rectifier diodes as power transferring elements, which is five in the circuit of
FIG. 19
, have been reduced to four by using a boost-type PWM converter. The AC power supply
1
passes through the reactor
106
to be inputted into a rectifier bridge circuit of which the lower arm is configured of the switching elements
3
a
,
3
b
and the rectifier diodes
2
a
,
2
b
and of which the upper arm is configured of the high speed diodes
4
a
and
4
b
. To the output of the rectifier bridge circuit, in the same way as the case of
FIG. 19
, a smoothing capacitor
7
, a load
8
and resistances
9
a
and
9
b
for detecting the output voltage are connected. In addition, a current sensor
213
is provided in order to detect the input current wave form and a transformer
211
is provided in order to detect the input voltage wave form. In order to gain input current wave form information |Iac| in the same way as the case of
FIG. 19
, diode bridge circuits
251
a
,
251
b
,
251
c
and
251
d
, are provided of which the result is sent to the control circuit
110
. Similarly in order to gain input voltage wave form information |Vac| in the same way as in the case of
FIG. 19
, diode bridge circuits
212
a
,
212
b
,
212
c
and
212
d
are provided of which the result is sent to the control circuit
110
. The processing configuration of the control circuit
110
is the same as that of FIG.
21
.
PROBLEMS TO BE SOLVED BY THE INVENTION
In the former as described in the prior art, however, the output of the AC power supply is rectified one time by a rectifier diode circuit and after that the boost converter circuit is operated, therefore, there is the problem that the number of elements through which the main circuit current passes is large in the circuit which causes a large basic loss.
In the latter as described in the prior art, though the number of elements through which the main circuit current passes is smaller, the detection of the input voltage wave form of the detection of the input current wave form are complicated and large-scaled. Because of this complication of the detection the consumption power for the detection cannot be so small as not to be taken into account. Also, there are many problems such that the large number of switching elements makes it easy to increase noise.
In either case, with respect to the main circuit configuration, no methods for easily gaining a high power factor, for maintaining the high efficiency, which are common basic problems to be solved, or for safe operation at the time of power variation are disclosed.
Considering such problems of conventional converter circuits, it is the purpose of the present invention to provide a converter circuit which can reduce the number of elements through which the main circuit current passes in the circuit with small losses in the main circuit, furthermore so as to additionally reduce the sensing circuit loss and to aim at an increase in effectiveness and which can implement miniaturization, loss reduction or noise reduction to gain a high power factor with a simple configuration.
MEANS FOR SOLVING PROBLEMS
A simple phase PWM converter circuit is configured so that two types of diodes of rectifier diodes for a low forward voltage drop and high speed diodes having a fast recovery function as well as switching elements are used to control the pulse width modulation, according to claims
1
to
8
,
19
and
20
of the present invention, which correspond to each aspect of the invention in the following:
(1) In order to miniaturize the detection circuit, which should correspond to a plurality of power supply frequencies, the input AC voltage is, for example, short circuited to the primary side of one photocoupler with resistance elements and the voltage of the secondary side of the photocoupler is inputted to the control circuit in the configuration so that frequency Fac or period Tac of the input AC voltage is calculated out from the reverse period of the voltage of the secondary side of the photocoupler in order to determine the input frequency.
(2) In order to reduce the loss from the detection circuit, the times of (2·Ton+2·Toff+Tac)/4 and (2·Ton+2·Toff+3·Tac)/4 are set at the zero cross time of the AC input voltage using the period Tac calculated out of the on time Ton and off time Toff of the secondary side of the photocoupler.
(3) In order to operate stably against the variation of the power supply, the period calculated out of the on time and the off time of the secondary side of the photocoupler is used to predict the next on time and off time so as to finally modify the prediction time of the subsequent on time and off time based on the polarity of the difference between the next on time and off time which are actually detected.
(4) To simplify the configuration of the control circuit., time measurement through the calculation of the respective times is carried out with a period which becomes the pulse width modulation control period.
(5) To implement the high power factor, the control means inputs output information of the secondary side of the photocoupler for each period so as to confirm the on condition or the off condition continuously for n times and, after that, the peak time and the zero cross time are calculated out as described above among which the time required for “n−1” input processing proceeds to the front to calculate out the above described time.
(6) (19) (20) To reduce ma
Doyama Yoshiaki
Matsushiro Hideo
Ogawa Masanori
Ueda Mitsuo
Yoshioka Kaneharu
Laxton Gary L.
Matsushita Electric - Industrial Co., Ltd.
Smith , Gambrell & Russell, LLP
Wong Peter S.
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