Voltage feed-forward compensation and voltage feedback compensation for switched mode power supplies

Patent metadata

Field	Value
Publication number	US-9397578-B2
Application number	US-201214379098-A
Country	US
Kind code	B2
Filing date	Feb 17, 2012
Priority date	Feb 17, 2012
Publication date	Jul 19, 2016
Grant date	Jul 19, 2016

Abstract

A digital control unit generates a control signal to control a duty cycle of a switched mode power supply such that a faster response to an input voltage transient is achieved. The digital control unit comprises a feedback compensator, a feed forward compensator, a transient detector, and a controller. The transient detector receives a signal indicative of the input voltage of the switched mode power supply and detects transients on the received signal. The feedback compensator receives a signal indicative of the output voltage of the switched mode power supply and adjusts the control signal. The feed forward compensator receives a signal indicative of the input voltage of the switched mode power supply, performs a relatively fast, but coarse, adjustment of the control signal, and then performs a more accurate, but relatively slow, adjustment of the control signal.

First claim

The invention claimed is:

1. A method of generating a digital control signal for controlling a duty cycle of a switched mode power supply, the method comprising:
receiving a signal indicative of an input voltage of the switched mode power supply;
receiving a signal indicative of an output voltage of the switched mode power supply;
detecting a transient on the received signal indicative of the input voltage of the switched mode power supply; and
in response to the detection of said transient:
performing a voltage feedback adjustment of a control signal for controlling the duty cycle of the switched mode power supply by adjusting the control signal in dependence upon the signal indicative of the output voltage;
in a first stage of feed forward compensation, performing a coarse voltage feed forward adjustment of the control signal for controlling the duty cycle of the switched mode power supply by setting a value of the control signal to a first value derived by performing a first at least one bit shift operation on the value of the control signal; and
in a second stage of feed forward compensation, performing a more accurate voltage feed forward adjustment of the control signal for controlling the duty cycle of the switched mode power supply by setting the value of the control signal to a second value calculated in dependence upon the signal indicative of the input voltage of the switched mode power supply;
wherein the first and second stages of the feed forward compensation are performed such that the control signal is set to the first value derived in the first stage before the control signal is set to the second value calculated in the second stage.

2. The method according to claim 1 , wherein the coarse and more accurate voltage feed forward adjustments of the control signal are performed such that:
in a first switch cycle of the switch mode power supply:
the first value for the control signal is derived by performing the first at least one bit shift operation on the value of the control signal, and the first value is stored for subsequent application; and
calculation is started for the second value of the control signal in dependence upon the signal indicative of the input voltage of the switched mode power supply;

in a second switch cycle of the switch mode power supply, the second switch cycle being a next switch cycle after the first switch cycle:
the control signal is adjusted by applying the first value for the control signal stored during the first switch cycle; and
calculation of the second value of the control signal is completed and the calculated second value is stored for subsequent application; and

in a third switch cycle of the switch mode power supply, the third switch cycle being a next switch cycle after the second switch cycle:
the control signal is adjusted by applying the second value for the control signal stored during the second switch cycle.

3. The method according to claim 2 , wherein, the voltage feedback adjustment of the control signal is performed in at least one of the first switch cycle and the second switch cycle.

4. The method according to claim 2 , wherein the first switch cycle comprises a switch cycle during which the transient is detected.

5. The method according to claim 2 , further comprising:
detecting if the transient is still present on the signal indicative of the input voltage of the switched mode power supply after the voltage feedback adjustment of the control signal, the coarse voltage feed forward adjustment of the control signal, and the more accurate voltage feed forward adjustment of the control signal have been performed; and
in response to the detection of the transient after the voltage feedback adjustment, the coarse voltage feed forward adjustment, and the more accurate voltage feed forward adjustment have been performed:
performing a further coarse voltage feed forward adjustment of the control signal by adjusting the control signal to a third value derived by performing a second at least one bit shift operation on the value of the control signal so as to change the value of the control signal by a predetermined amount selected in dependence upon a size of the detected transient; and
performing a further more accurate voltage feed forward adjustment of the control signal by setting the control signal to a fourth value calculated in dependence upon the signal indicative of the input voltage of the switched mode power supply.

6. The method according to claim 5 , wherein the further coarse and further more accurate voltage feed forward adjustments of the control signal are performed such that:
in the third switch cycle of the switch mode power supply:
the third value for the control signal is derived by performing the second at least one bit shift operation on the value of the control signal to derive the third value for the control signal adjusted by the predetermined amount selected in dependence upon the size of the detected transient, and the derived third value is stored for subsequent application; and
calculation is started for the fourth value of the control signal in dependence upon the signal indicative of the input voltage of the switched mode power supply;

in a fourth switch cycle of the switch mode power supply, the fourth switch cycle being a next switch cycle after the third switch cycle:
the control signal is adjusted by applying the third value for the control signal stored during the third switch cycle; and
calculation of the fourth value of the control signal is completed and the calculated fourth value is stored for subsequent application; and

in a fifth switch cycle of the switch mode power supply, the fifth switch cycle being a next switch cycle after the fourth switch cycle:
the control signal is adjusted by applying the fourth value stored during the fourth switch cycle.

7. The method according to claim 6 , wherein voltage feedback adjustment of the control signal is performed in at least one of the third switch cycle and the fourth switch cycle.

8. The method according to claim 1 , wherein the first value for the coarse voltage feed forward adjustment of the control signal is calculated by performing a plurality of bit shift operations on the value of the control signal and combining a result of each shift.

9. A digital control unit operable to control a duty cycle of a switched mode power supply, the digital control unit comprising:
a feedback compensator arranged to receive a signal indicative of an output voltage of the switched mode power supply and operable to adjust a control signal for controlling the duty cycle of the switched mode power supply in dependence upon the signal indicative of the output voltage;
a feed forward compensator operable to receive a signal indicative of an input voltage of the switched mode power supply and operable to perform a coarse adjustment of the control signal for controlling the duty cycle of the switched mode power supply by setting a value of the control signal to a first value derived by performing a first at least one bit shift operation on the value of the control signal and operable to perform a more accurate adjustment of the control signal for controlling the duty cycle of the switched mode power supply by setting the value of the control signal to a second value calculated in dependence upon the signal indicative of the input voltage;
a transient detector operable to receive the signal indicative of the input voltage of the switched mode power supply and operable to detect a transient on the received signal indicative of the input voltage of the switched mode power supply; and
a controller operable to control the operation of the feedback compensator and the feed forward

Assignees

• Karlsson Magnus
• Kullman Anders
• Malmberg Jonas
• Wahledow Fredrik
• Ericsson Telefon Ab L M

Inventors

• Karlsson Magnus
• Kullman Anders
• Malmberg Jonas
• Wahledow Fredrik

Classifications

• H02M2001/0022

  Electricity · mapped topic

• H02M1/14 Primary

  Arrangements for reducing ripples from DC input or output · CPC title

• H02M3/33546 Primary

  with automatic control of the output voltage or current (H02M3/33561 takes precedence) · CPC title

• H02M2001/0012

  Electricity · mapped topic

• H02M2001/0016

  Electricity · mapped topic