Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
1998-05-19
2001-03-13
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S058000, C363S098000
Reexamination Certificate
active
06201716
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a controller for controlling switching elements of a power supplying apparatus for supplying power to a load such as a three-phase motor through the switching elements.
2. Description of the Prior Art
FIG. 7
shows a circuit diagram of the main circuit of a power supplying apparatus controlled by a prior art controller of power supplying apparatus. Referring to
FIG. 7
, reference numeral
1
denotes a three-phase motor as a load. Reference numeral
2
denotes a DC power source. Reference numeral
3
denotes the switching element on the positive-phase side of the U-phase circuit. Reference numeral
4
denotes the switching element on the negative-phase side of the U-phase circuit. Reference numeral
5
denotes the switching element on the positive-phase side of the V-phase circuit. Reference numeral
6
denotes the switching element on the negative-phase side of the V-phase circuit. Reference numeral
7
denotes the switching element on the positive-phase side of the W-phase circuit. Reference numeral
8
denotes the switching element on the negative-phase side of the W-phase circuit. The switching elements
3
to
8
are rendered conductive when the gate voltage is at an L level. Reference numeral
9
denotes an interface circuit responsive to control signals from a controller
10
for controlling the switching elements
3
to
8
. Reference numeral
10
denotes the controller.
FIG. 8
is a block diagram showing structure of the controller
10
. Referring to
FIG. 8
, reference numerals
11
u
,
11
v
, and
11
w
denote timers. The timer
11
u
, upon receipt of a control command for the switching elements
3
and
4
from a speed controlling circuit, not shown, starts counting time and, at the same time, outputs a signal at an H level. Thereafter, it, when the counted time reaches a preset period of time T
1
, outputs a signal at an L level. The timers
11
v
and
11
w
perform the same functions as the timer
11
u
does, except that the control object are switching elements
5
and
6
and switching elements
7
and
8
, respectively. Reference numerals
12
u
,
12
v
, and
12
w
denote short-circuit preventing timers. The short-circuit preventing timers
12
u
,
12
v
, and
12
w
, when the signal levels of the signals outputted from the timers
11
u
,
11
v
, and
11
w
change, respectively, from H level to L level, output a pulse signal with a pulse width of T
2
(T
2
corresponds to the short-circuit preventing period of time). Reference numerals
13
u
,
13
v
, and
13
w
denote flip-flops. The flip-flops
13
u
,
13
v
, and
13
w
, when the signal level of the signal outputted from the timers
11
u
,
11
v
, and
11
w
, respectively, changes from H level to L level, invert the signal level of the signal outputted therefrom.
Further, reference numerals
14
u
,
14
v
, and
14
w
denote flip-flops. The flip-flops
14
u
,
14
v
, and
14
w
, when the signal level of the signal outputted from the short-circuit preventing timers
12
u
,
12
v
, and
12
w
, respectively, changes from H level to L level, output a signal having a different signal level from the signal level of the signal outputted from the Q terminal of the flip-flops
13
u
,
13
v
, and
13
w
. Reference numerals
15
u
,
15
v
, and
15
w
denote NAND circuits. To one input terminals of the NAND circuits
15
u
,
15
v
, and
15
w
, the signals outputted from the flip-flops
14
u
,
14
v
, and
14
w
are inputted, respectively, and to the other input terminals, the signals outputted from the Q terminals of the flip-flops
13
u
,
13
v
, and
13
w
are inputted, respectively. Reference numerals
16
u
,
16
v
, and
16
w
denote flip-flops. The flip-flops
16
u
,
16
v
, and
16
w
, when the signal level of the signal outputted from the short-circuit preventing timers
12
u
,
12
v
, and
12
w
changes from H level to L level, respectively, output a signal having a signal level different from the signal level of the signal outputted from the QB terminal of the flip-flops
13
u
,
13
v
, and
13
w
. Reference numerals
17
u
,
17
v
, and
17
w
denote NAND circuits. To one input terminals of the NAND circuits
17
u
,
17
v
, and
17
w
, the signals outputted from the flip-flops
16
u
,
16
v
, and
16
w
are inputted, respectively, and to the other input terminals, the signals outputted from the QB terminals of the flip-flops
13
u
,
13
v
, and
13
w
are inputted, respectively. Reference numerals
18
u
,
18
v
, and
18
w
denote terminals on the positive-phase side of the U-phase, V-phase, and W-phase, respectively. Reference numerals
19
u
,
19
v
, and
19
w
denote the terminals on the negative-phase side of the U-phase, V-phase, and W-phase, respectively.
Now, operations will be described. Since the operations of the V-phase and W-phase are the same as the operations of the U-phase, description will only be given on the operations of the U-phase and description on the operations of the V-phase and W-phase will be omitted.
First, when driving a three-phase motor
1
, it is necessary to supply AC power to the three-phase motor
1
. Especially when it is required to control the revolving speed of the three-phase motor
1
to change over a wide range, sometimes, a power supplying apparatus in which AC power is once converted to DC power and then the DC power is inverted to desired AC power and supplied to the three-phase motor
1
is used (in
FIG. 7
, the portion converting AC power to DC power is omitted).
In the use of such a power supplying apparatus for supplying power by once converting AC power to DC power and then converting the DC power back to AC power, it becomes possible to supply desired AC power to the three-phase motor
1
by suitably controlling the firing angles of the switching elements
3
to
8
. However, when the switching element
3
on the positive-phase side and the switching element
4
on the negative-phase side of the U-phase are rendered conductive at the same time, for example, it short-circuits the DC power source
2
in a no-load condition and, hence, it sometimes occurs that a large current flows from the DC power source
2
to ground through the switching elements
3
and
4
and, thereby the switching elements
3
,
4
and the like are damaged.
Therefore, in order to prevent the switching element
3
on the positive-phase side and the switching element
4
on the negative-phase side from becoming conductive at the same time, first, when the timer
11
U receives a control command for the switching elements
3
and
4
from a speed control circuit, not shown, at the point of time A as shown in
FIG. 9
, it starts counting time and, at the same time, outputs a signal at an H level and, when the counted time reaches a preset period of time T
1
, it outputs a signal at an L level (in the example of
FIG. 9
, the counted time reaches the preset period of time T
1
at the point of time B).
When the output signal from the timer
11
u
changes from H level to L level at the point of time B, the short-circuit preventing timer
12
u
is triggered by the trailing edge and outputs a pulse signal with a pulse width corresponding to a short-circuit preventing period of time T
2
.
The flip-flop
13
u
is also triggered by the trailing edge of the output signal of the timer
11
u
and inverts the signal levels of its output signals (in the example of
FIG. 9
, the signal level of the output signal from the Q terminal is changed from L level to H level and the signal level of the output signal from the QB terminal is changed from H level to L level).
Further, since the signal level of the output signal from the QB terminal of the flip-flop
13
u
changes from H level to L level at the point of time B, the NAND circuit
17
u
is triggered by the trailing edge and changes the signal level of its output signal from L level to H level.
Thus, a signal at an H level is outputted from the terminal
19
u
on the negative phase side of the U-phase to the interface circuit
9
at the point of time B, and hence, the swi
Burns Doane , Swecker, Mathis LLP
Mitsubishi Denki & Kabushiki Kaisha
Vu Bao Q.
Wong Peter S.
LandOfFree
Controller of power supplying apparatus with short circuit... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Controller of power supplying apparatus with short circuit..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Controller of power supplying apparatus with short circuit... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2491024