COMPENSATION FREE MODULATION FOR POWER CONVERTERS
A method is provided for controlling a power stage of a power converter configured to generate an output voltage from an input voltage according to a control law controlling a switchable power stage. The method includes generating a pulsed control signal for switching the power stage and translating the pulsed control signal in phase relative to a constant frequency clock signal. The pulse is translated forward to increase charge in a cycle. The pulse is translated backward to decrease charge in a cycle. Thus, this method of charge control does not require compensation.
1 . A control method for a power converter having a switched power stage configured to generate an output voltage from an input voltage according to a pulsed control signal controlling a switching of the switched power stage, the method comprising:
generating a pulsed control signal for switching the power stage by translating a pulse of a constant frequency PWM signal in phase relative to a corresponding steady state pulse of the constant frequency PWM signal.
2 . The method according to claim 1 , wherein translating a pulse of the constant frequency PWM signal comprises translating the pulse forward to increase charge in a cycle.
3 . The method according to claim 1 , wherein translating a pulse of the constant frequency PWM signal comprises translating the pulse backward to decrease charge in a cycle.
4 . The method according to claim 1 , further comprising:
varying a pulse width of the pulsed control signal so that a square of the pulse width varies in dependence of a voltage error derived from a difference between a reference voltage and the output voltage to further increase or decrease charge in a cycle.
5 . The method according to claim 4 , wherein:
the pulse width of the pulsed control signal is varied such that a resulting charge Q of a cycle is given by
Q
=
V
in
-
V
out
2
L
(
V
in
V
out
)
t
p
2
,
wherein V in is the input voltage, V out is the output voltage, L is an inductance of the switchable power stage and t p is the pulse width of the pulsed control signal.
6 . The method according to claim 4 , wherein: the pulse width of the pulse control signal is varied by augmenting a steady state pulse width t ss by an additional on-time t d such that an additional charge Q d of a cycle is given by
Q
d
=
V
in
-
V
out
2
L
(
V
in
V
out
)
t
d
t
ss
when the steady state pulse width t ss is determined otherwise.
7 . The method according to claim 4 , further comprising:
determining the steady state pulse width t ss prior to generating the pulsed control signal.
8 . The method according to claim 7 , further comprising:
attempting to detect a steady state or quasi-steady state shift in current; and
adjusting the pulse width to offset a pulse translation resulting from a steady state or quasi-steady state shift when a steady state or quasi-steady state shift has been detected.
9 . A power converter comprising: a switched power stage configured to generate an output voltage from an input voltage, and a controller configured to generate a pulsed control signal for switching the power stage by translating a pulse of pulsed constant frequency PWM signal in phase relative to a corresponding steady state pulse of the constant frequency PWM signal.
10 . The power converter according to claim 9 , wherein the controller is configured to translate the pulse forward to increase charge in a cycle or to translate the pulse backward to decrease charge in a cycle.
11 . The power converter according to claim 9 , wherein the controller is configured to vary a pulse width of the pulsed control signal so that a square of the pulse width varies in dependence upon a voltage derived from a difference between a reference voltage and the output voltage.
12 . The power converter according to claim 10 , wherein the controller is further configured to vary the pulse width of the pulse control signal such that a resulting charge Q of a cycle is given by
Q
=
V
in
-
V
out
2
L
(
V
in
V
out
)
t
p
2
,
wherein V in is the input voltage, V out is the output voltage, L is an inductance of the switchable power stage and t p is the pulse width of the pulsed control signal.
13 . The power converter according to claim 9 , wherein the controller is configured to vary the pulse width of the pulsed control signal by augmenting a steady state pulse width t ss by an additional on-time t d such that an additional charge Q d of a capacitance of the switchable power stage is given by
Q
d
=
V
in
-
V
out
2
L
(
V
in
V
out
)
t
d
t
ss
when the steady state pulse width t ss is determined otherwise.
14 . The power converter according to claim 13 , further comprising means for determining the steady state pulse width t ss prior to generating the pulse control signal.
15 . The power converter according to claim 9 , further comprising means to detect a steady state or quasi-steady state shift in current and means to adjust the pulse width to offset a pulse translation resulting from a steady state or quasi-steady state shift when a steady state or quasi-steady state shift has been detected.