Sensor-less, low frequency adaptive current limiter and methods for limiting inductive current using the same
View Patent ↗Devices and systems that use an adaptively limited PWM duty-cycle to control a circuit and methods and control programs to operate and to control the devices and systems to adaptively limit the PWM duty-cycle are disclosed. The devices and systems are capable of adjusting the duty-cycle such that the actual inductor current in the next cycle is precisely limited. Specifically, a maximum allowable duty-cycle for time interval N+1 is estimated during time interval N. When the duty-cycle is applied to the circuit at time interval N+1, the peak inductor current is kept below a maximum allowable inductor current level.
1. A method of controlling inductor current levels during a second time interval (N+1) having a beginning and a duty-cycle, the second time interval (N+1) following a first time interval (N), the method comprising:
sampling a first inductor current level (I(n)) at or substantially at the beginning of the first time interval (N); and
controlling the duty-cycle in the second time interval (N+1) so that a peak inductor current level, (I p (n+1)), during said second time interval (N+1) does not exceed a predetermined maximum current level, (I LIMIT ),
wherein controlling the duty-cycle includes calculating a maximum allowable duty-cycle using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I(n) is current at or near the beginning of the first time interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the first time interval (N) that was calculated during time interval (N−1) sequentially before the first time interval (N).
2. A method of calculating an allowable duty-cycle for a subsequent pulse width modulation interval (N+1), having a beginning, the subsequent pulse width modulation interval (N+1) following a first pulse width modulation interval (N), the method comprising:
sampling a first inductor current level, (I(n)), at or substantially at near the beginning of the first pulse width modulation interval (N); and
sampling a second inductor current level (I(n+1), at or substantially at near the beginning of the second pulse width modulation interval (N+1);
estimating a value for the second inductor current level (I(n+1)) at the end of first pulse width modulation interval (N); and
measuring one or more voltage inputs, (V i (n)) and one or more voltage outputs, (V o (n)), wherein the method includes calculating a maximum allowable duty-cycle (D MAX (n)) using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I LIMIT is a predetermined maximum current level;
I(n) is current at or substantially at the beginning of the first pulse width modulation interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(N−1) is a duty-cycle for the first pulse width modulation interval (N) calculated during a pulse width modulation interval (N−1) that occurs sequentially before the first pulse width modulation interval (N).
3. A system for calculating an allowable duty-cycle for a subsequent pulse width modulation interval (N), the pulse width modulation interval (N) following a first pulse width modulation interval (N−1), the system comprising:
means for sampling a first inductor current level, (I(n)), at or substantially at the beginning of a first pulse width modulation interval (N);
means for sampling a second inductor current level (I(n+1)) at or substantially at the beginning of the subsequent pulse width modulation interval (N+1);
means for estimating a value for the first inductor current at or substantially at the end of the first pulse width modulation interval (N);
means for measuring one or more voltage inputs (V i (n)) and one or more voltage outputs (V o (n)); and
means for calculating a maximum allowable duty-cycle using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I LIMIT is a predetermined maximum current level;
I (n) is current at or substantially at the beginning of the first pulse width modulation interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the first pulse width modulation interval (N) calculated during a pulse width modulation interval (N−1) that occurs sequentially before the first pulse width modulation interval (N).
4. A device for controlling inductor current levels in a circuit, the device comprising:
a controller that calculates a maximum allowable duty-cycle so that a peak current level (I p (n−1)) during a second time interval (N+1), the second time interval (N+1) sequentially following a first time interval (N), does not exceed a predetermined maximum current level, (I LIMIT ); and
a duty-cycle limiter for controlling the duty-cycle of the circuit for said secondary time interval (N+1),
wherein the controller is adapted to calculate the maximum allowable duty-cycle (D MAX (n)) by sampling a first inductor current level (I(n)) at or substantially at a beginning of the first time interval (N); by estimating a value for the first inductor current at the end of said first time interval (N); and by measuring one or more voltage inputs (V i (n)) and one or more voltage outputs (V o (n)), and
wherein the controller calculates a maximum allowable duty-cycle using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I(n) is current at or substantially at the beginning of the first time interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the first time interval (N) calculated during a time interval (N−1) that occurs sequentially before the first time interval (N).
5. A device for calculating an allowable duty-cycle for a subsequent pulse width modulation interval (N+1), the device comprising:
means for sampling a first inductor current level (I(n)) at or substantially at a beginning of a first pulse width modulation interval (N);
means for sampling a second inductor current level (I(n+1)) at or substantially at a beginning of the subsequent pulse width modulation interval (N+1);
means for estimating a value for the second inductor current level at or substantially at an end of the first pulse width modulation interval (N); and
means for measuring one or more voltage inputs (V i (n)) and one or more voltage outputs (V o (n)),
wherein the device calculates a maximum allowable duty-cycle using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I LIMIT is a predetermined maximum current level;
I (n) is current at or substantially at the beginning of the subsequent pulse width modulation interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the first pulse width modulation interval (N) calculated during a pulse width modulation interval (N−1) that occurs sequentially before the first pulse width modulation interval (N).
6. A method of controlling inductor current levels during a subsequent time interval (N+1), the subsequent time interval (N+1) sequentially following a first time interval (N) having a beginning and an end, the method comprising:
measuring one or more voltage inputs (V i (n)) and one or more voltage outputs (V o (n));
sampling a first inductor current level (I(n)) at or substantially at the beginning of the first time interval (N);
estimating a value for the first inductor current at or substantially at the end of first time interval (N);
estimating a duty-cycle for the subsequent time interval (N+1) using the estimated value of the first inductor current (I(n)), wherein estimating the duty-cycle includes calculating the maximum allowable duty-cycle (D MAX (n)) using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I(n) is current level measured at or substantially at the beginning of the first time interval (N),
L is inductance,
f s is frequency,
V i (n) is one or more input voltages,
V o (n) is one or more output voltages, and
D(n−1) is a duty-cycle for the first time interval (N) that was calculated during a time interval (N−1) sequentially before the first time interval (N); and
controlling the duty-cycle for the subsequent time interval (N+1) so that a peak inductor current level (I 1 (n+1)) during said subsequent time interval (N+1) does not exceed a predetermined maximum current level (I LIMIT ).
7. The method as recited in claim 6 , wherein estimating the duty-cycle for the subsequent time interval (N+1) includes calculating a maximum allowable duty-cycle (D MAX (n)) during said first time interval (N).
8. The method as recited in claim 6 , wherein sampling the first inductor current level (I(n)) at or substantially at the beginning of the first time interval (N) includes sampling an inductor current level immediately before the beginning of the first time interval (N) or by sampling an inductor current level immediately after the beginning of the first time interval (N).
9. A method of calculating an allowable duty-cycle for a subsequent pulse width modulation interval (N+1), having a beginning, the subsequent pulse width modulation interval (N+1) sequentially following a first pulse width modulation interval (N) having a beginning and an end, the method comprising:
measuring one or more voltage inputs (V i (n)) and one or more voltage outputs (V o (n));
sampling a first inductor current level (I(n)) at or substantially at the beginning of the first pulse width modulation interval (N);
estimating a value for the first inductor current level at of substantially at the end of first pulse width modulation interval (N); and
estimating the allowable duty-cycle for the subsequent pulse width modulation interval (N+1) during said first pulse width modulation interval (N) using said estimated value of the first inductor current such that a peak inductor current level (I p (n+1)) during said subsequent time interval (N+1) does not exceed a predetermined maximum current level (I LIMIT ), wherein estimating the duty-cycle includes calculating a maximum allowable duty-cycle (D MAX (n)) during said first time interval (N) using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I(n) is current level measured at or substantially at the beginning of the first time interval (N),
L is inductance,
f s is frequency,
V i (n) is one or more input voltages,
V o (n) is one or more output voltages, and
D(n−1) is a duty-cycle for the first time interval (N) that was calculated during a time interval (N−1) sequentially before the first time interval (N).
10. The method as recited in claim 9 , wherein sampling the first inductor current level includes sampling the first inductor current level immediately before the beginning of the first pulse width modulation interval or immediately after the beginning of the first pulse width modulation interval.
11. A control program embodied in a computer-readable media that is executable on a processing device for controlling inductor current levels in a circuit during a second time interval (N+1)) that sequentially follows a first time interval (N), the program providing machine code to:
measure one or more voltage inputs (V i (n)) and one or more voltage outputs (V o (n));
sample a first inductor current level (I(n)) at or substantially at a beginning of the first time interval (N);
estimate a value for the first inductor current level at or substantially at an end of first time interval (N);
estimate a duty-cycle for the second time interval (N+1) during the first time interval (N) using the estimated value of the first inductor current level so that a peak inductor current level (I p (n+1)) during said second time interval (N+1) does not exceed a predetermined maximum current level (I LIMIT );
control the duty-cycle for the second time interval (N+1) so that the peak inductor current level (I p (n+1)) during said second time interval (N+1) does not exceed a predetermined maximum current level (I LIMIT ); and
providing machine code to control the duty-cycle for the second time interval (N+1) by calculating a maximum allowable duty-cycle (D MAX (n)) during the first time interval (N) for use in the second time interval (N+1) and to calculate the maximum allowable duty-cycle using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I(n) is current at or substantially at the beginning of the first time interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the first time interval (N) calculated during a time interval (n−1) sequentially before the first time interval (N).
12. The program as recited in claim 11 , further providing machine code that samples the first inductor current level by sampling the first inductor current level immediately before the beginning of the first time interval or by sampling the first inductor current level immediately after the beginning of the first time interval.
13. A control program embodied in a Computer-readable medium that is executable on a processor, the program providing machine code to calculate an allowable duty-cycle for a subsequent pulse width modulation interval (N+1), the subsequent pulse width modulation interval (N+1) sequentially following a first pulse width modulation interval (N) having a beginning and an end, the machine code providing machine code to:
measure one or more voltage inputs (V i (n)) and one or more voltage outputs (V o (n));
sample a first inductor current level (I(n)) at or substantially at the beginning of a first pulse width modulation interval (N); and
estimate a value for the first inductor current level at or substantially at the end of the first pulse width modulation interval (N);
estimate the allowable duty-cycle (D(n)) for the subsequent pulse width modulation interval (N+1) during the first pulse width modulation interval (N) using said estimated value of the first inductor current,
wherein machine code for estimating the allowable duty-cycle includes calculating a maximum allowable duty-cycle (D MAX (n)) using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I LIMIT is a predetermined maximum current level;
I(n) is the first inductor current level current at or substantially at the beginning of the first pulse width modulation interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the first pulse width modulation interval (N), which was estimated during a pulse width modulation interval (N−1) sequentially before the first pulse width modulation interval (N).
14. The control program as recited in claims 13 , the machine code further providing machine code to:
control the allowable duty-cycle ((D (n)) for the subsequent pulse width modulation interval (N+1) so that a peak inductor current level (I p (n+1)) during said subsequent time interval (N+1) does not exceed a predetermined maximum current level (I LIMIT )
15. A system for controlling inductor current levels in a circuit, the system comprising:
a converter having a duty-cycle for delivering power to a load;
a controller that calculates a maximum allowable duty-cycle (D MAX (n)) during a first time interval (N) so that a peak current level (I p (n+1)) during a subsequent time interval (N+1) does not exceed a predetermined maximum current level (I LIMIT ); and
a duty-cycle limiter that is adapted to control the converter's duty-cycle during the subsequent time interval (N+1),
wherein the controller calculates the maximum allowable duty-cycle for the subsequent time interval (N+1) during the first time interval (N) using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I(n) is current at or substantially at the beginning of the first time interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the first time interval (N) calculated during a time interval (N−1) sequentially before the first time interval (N).
16. The system as recited in claim 15 , wherein the controller is structured and arranged to calculate the maximum allowable duty-cycle (D MAX (n)) during the first time interval (N) by sampling a first inductor current level (I(n)) at or substantially at a beginning of the first time interval (N); and by estimating a value for the first inductor current level at or substantially at the end of the first time interval (N).
17. A system for calculating an allowable duty-cycle for a subsequent pulse width modulation interval (N+1), the subsequent pulse width modulation interval (N+1) following a first pulse width modulation interval (N), the system comprising:
means for measuring one or more voltage inputs (V i (n)) and one or more voltage outputs (V o (n));
means for sampling a first inductor current level (I(n)) at or substantially at the beginning of a first pulse width modulation interval (N);
means for estimating a value for the first inductor current at or substantially at the end of the first pulse width modulation interval (N);
means for calculating the allowable duty-cycle using the estimated value for the first inductor current so that a peak current level (I p (n+1)) during the subsequent time interval (N+1) does not exceed a predetermined maximum current level (I LIMIT ); and
a duty-cycle limiter that is adapted to control the duty-cycle during the subsequent pulse width modulation interval (N+1),
wherein the calculating means calculates the maximum allowable duty-cycle using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I(n) is current at or substantially at the beginning of the subsequent pulse width modulation interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the subsequent pulse width modulation interval (N) which was estimated during a pulse width modulation interval (N−1) sequentially before the first pulse width modulation interval (N).
18. A current limiting device for controlling inductor current levels of a circuit, the device comprising:
means for sampling a first inductor current level (I n)) at or substantially at a beginning of a first time interval (N);
means for estimating a value for the first inductor current level at or substantially at an end of the first time interval (N);
means for calculating a maximum allowable duty-cycle for a subsequent time interval (N+1) that sequentially follows a first time interval (N) using the estimated value of the first inductor current level so that a peak current level (I p (n+1)) does not exceed a predetermined maximum current level (I LIMIT ); and
means for controlling the duty-cycle of the circuit during said subsequent time interval (N+1),
wherein the calculating means calculates the maximum allowable duty-cycle using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I(n) is current at or substantially at the beginning of the first time interval (N);
L is inductance;
f s is frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the first time interval (N) calculated during a time interval (N−1) sequentially before the first time interval (N)
19. The device as recited in claim 18 , wherein the calculating means calculates the maximum allowable duty-cycle (D MAX (n)) for use in the subsequent time interval (N+1) during the first time interval (N).
20. A system for controlling inductor current levels in a circuit, the system comprising:
a converter for delivering power to a load during a duty-cycle;
a duty-cycle limiter for controlling the duty-cycle of the converter for a second time interval (N+1), the second time interval (N+1) following a first time interval (N); and
a controller that calculates the duty-cycle so that a peak current level (I p (n+1)) during the second time interval (N+1) does not exceed a predetermined maximum current level, (I LIMIT ),
wherein the duty-cycle limiter controls the duty-cycle during time interval (N+1) using a maximum allowable duty-cycle, (D MAX (n)) that is calculated using the equation:
D
MAX
(
n
)
=
(
I
LIMIT
-
I
(
n
)
)
L
·
f
s
V
i
(
n
)
+
V
o
(
n
)
V
i
(
n
)
(
1
-
D
(
n
-
1
)
)
-
1
where:
I (n) is current at or substantially at the beginning of the first time interval (N);
is inductance;
fis frequency;
V i (n) is one or more input voltages;
V o (n) is one or more output voltages; and
D(n−1) is a duty-cycle for the first time interval (N) calculated during a time interval (N−1) that occurs sequentially before the first time interval (N).