System and method for input current shaping in a power converter
View Patent ↗A power converter delivers electrical power from an electrical power source to a load according to a plurality of operation modes corresponding to different levels of input voltage or output current. The power converter comprises a power stage for delivering the electrical power from the power source to the load, a switch in the power stage that electrically couples or decouples the load to the power source, and a switch controller coupled to the switch for controlling the on-times and off-times of the switch according to the plurality of operation modes. Each of the operation modes correspond to associated ranges of at least one of an input voltage to the power converter and an output current from the power converter, where the associated ranges are different for each of the operation modes.
1. A method of shaping input current to a power converter, the method comprising:
the power converter determining waveform synthesis parameters based upon an input voltage signal and a reference waveform shape;
the power converter selecting one of a plurality of operation modes for controlling on-times and off-times of a switch in the power converter, the operation modes including a first operation mode selected if an input voltage to the power converter is in a first input voltage range, a second operation mode selected if the input voltage to the power converter is in a second input voltage range, and a third operation mode selected if an output current from the power converter is lower than a predetermined threshold current or if the on-times are lower than a predetermined threshold on-time; and
the power converter synthesizing the input current waveform in real time by controlling on-times and off-times of the switch based upon the determined waveform synthesis parameters and the selected operation modes.
2. The method of claim 1 , wherein the power converter is a flyback power converter and wherein:
the first operation mode controls the switch such that the power converter is operated in discontinuous conduction mode with fixed frequency with the on-times and off-times fixed; and
the second operation mode controls the switch such that the power converter is operated with variable frequency and variable duty cycle in critical discontinuous conduction mode with the on-times modulated by input instantaneous voltage and the off-times determined by requirements for the critical discontinuous conduction mode.
3. The method of claim 2 , wherein in the second operation mode the on-times are modulated by the input instantaneous voltage to keep a product of a squared duty ratio and a cycle time in the second operation mode to be constant and proportional to output power.
4. The method of claim 3 , wherein in the first operation mode the on-times and the off-times are fixed so that a product of a squared duty ratio and a cycle time in the first operation mode is constant and equal to the product in the second operation mode.
5. The method of claim 1 , wherein the first input voltage range corresponds to when the input voltage to the power converter is lower than an average of the input voltage and the second input voltage range corresponds to when the input voltage to the power converter is higher than the average of the input voltage.
6. The method of claim 1 , wherein the third operation mode controls the switch such that the power converter is operated in discontinuous conduction mode with the on-times and the off-times fixed.
7. The method of claim 6 , wherein the on-times and the off-times in the third operation mode are fixed and determined by pulse frequency modulation.
8. The method of claim 6 , wherein synthesizing the input current waveform in real time comprises:
generating a first on-time based on the reference waveform shape;
generating a second on-time based on the third operation mode;
selecting a larger one of the first and second on-times to generate a third on-time;
generating a fourth on-time based upon a current through the switch and the reference waveform shape;
selecting a smaller one of the third and fourth on-times as the on-time for the switch;
generating a first off-time based upon a control voltage indicating a difference between an output feedback voltage and a reference feedback voltage;
generating a second off-time for maintaining zero voltage switching;
generating a third off-time for the first operation mode to be equal to an off-time of an immediately preceding switching cycle of the second operation mode; and
selecting a largest one of the first, second, and third off-times as the off-time for the switch.
9. A power converter comprising:
a power stage for transferring electrical power from a power source to a load;
a switch in the power stage that electrically couples or decouples the load to or from the power source; and
a switch controller coupled to the switch for shaping input current to the power converter, the switch controller including;
a current shaper module for determining waveform synthesis parameters based upon an input voltage signal and a reference waveform shape;
an operation mode selector module for selecting one of a plurality of operation modes for controlling on-times and off-times of a switch in the power converter, the operation modes including a first operation mode selected if an input voltage to the power converter is in a first input voltage range, a second operation mode selected if the input voltage to the power converter is in a second input voltage range and a third operation mode selected if an output current from the power converter is lower than a predetermined threshold current or if the on-times are lower than a predetermined threshold on-time; and
a current waveform synthesizer module for synthesizing the input current waveform in real time by controlling on-times and off-times of the switch based upon the determined waveform synthesis parameters and the selected operation modes.
10. The power converter of claim 9 , wherein the power converter is a flyback power converter and wherein:
the first operation mode controls the switch such that the power converter is operated in discontinuous conduction mode with the on-times and off-times fixed; and
the second operation mode controls the switch such that the power converter is operated in critical discontinuous conduction mode with the on-times modulated by the input voltage and the off-times determined by requirements for the critical discontinuous conduction mode.
11. The power converter of claim 10 , wherein in the second operation mode the on-times are modulated by the input instantaneous voltage to keep a product of a squared duty ratio and a cycle time in the second operation mode to be constant and proportional to output power.
12. The power converter of claim 11 , wherein in the first operation mode the on-times and the off-times are fixed so that a product of a squared duty ratio and a cycle time in the first operation mode is constant and equal to the product in the second operation mode.
13. The power converter of claim 9 , wherein the third operation mode controls the switch such that the power converter is operated in discontinuous conduction mode with the on-times and the off-times fixed.
14. The power converter of claim 13 , wherein the on-times and the off-times in the third operation mode are fixed and determined by pulse frequency modulation.
15. The power converter of claim 9 , wherein the switch controller further includes a feedback signal generator for generating an analog feedback signal representing an output voltage of the power converter, the feedback signal generator including:
a first comparator for comparing a voltage sensed at an auxiliary winding of a transformer in the power stage with a constant zero voltage switching reference voltage to generate a first comparator output signal;
a second comparator for comparing the voltage sensed at the auxiliary winding of the transformer in the power stage with the analog feedback signal to generate a second comparator output signal;
a sampling module for determining delta differences between high and low edges of the first comparator output signal and the second comparator output signal;
a summation module for summing the delta differences to generate a digital feedback signal; and
a digital-to-analog converter for converting the digital feedback signal to the analog feedback signal.
16. The power converter of claim 9 , wherein the current waveform synthesizer module includes:
an adder for adding a control voltage indicating a difference between an output feedback voltage and a reference feedback voltage to a feed-forward voltage indicating a squared value of an average input voltage;
an on-time slope generator for generating an on-time ramp signal using an output of the adder;
a first comparator for comparing the on-time ramp signal with a reference voltage to generate on-times for the switch;
an off-time slope generator for generating an off-time ramp signal using the control voltage; and
a second comparator for comparing the off-time ramp signal with an off-time reference voltage to generate off-times for the switch.
17. The power converter of claim 9 , wherein the current waveform synthesizer module includes:
a multiplier for multiplying a control voltage indicating a difference between an output feedback voltage and a reference feedback voltage to a reference voltage;
an on-time slope generator for generating an on-time ramp signal based upon a feed-forward voltage indicating a squared value of an average input voltage;
a first comparator for comparing the on-time ramp signal with an output of the multiplier to generate on-times for the switch;
an off-time slope generator for generating an off-time ramp signal based upon the control voltage; and
a second comparator for comparing the off-time ramp signal with an off-time reference voltage to generate off-times for the switch.
18. A controller for controlling a power converter, the power converter including a power stage for transferring electrical power from a power source to a load and a switch in the power stage that electrically couples or decouples the load to or from the power source, wherein the controller is coupled to the switch for shaping input current to the power converter, the controller comprising:
a current shaper module for determining waveform synthesis parameters based upon an input voltage signal and a reference waveform shape;
an operation mode selector module for selecting one of a plurality of operation modes for controlling on-times and off-times of a switch in the power converter, the operation modes including a first operation mode selected if an input voltage to the power converter is in a first input voltage range, a second operation mode selected if the input voltage to the power converter is in a second input voltage range, and a third operation mode selected if an output current from the power converter is lower than a predetermined threshold current or if the on-times are lower than a predetermined threshold on-time; and
a current waveform synthesizer module for synthesizing the input current waveform in real time by controlling on-times and off-times of the switch based upon the determined waveform synthesis parameters and the selected operation modes.
19. The controller of claim 18 , wherein the power converter is a flyback power converter and wherein:
the first operation mode controls the switch such that the power converter is operated in discontinuous conduction mode with the on-times and off-times fixed; and
the second operation mode controls the switch such that the power converter is operated in critical discontinuous conduction mode with the on-times modulated by the input voltage and the off-times determined by requirements for the critical discontinuous conduction mode.
20. The controller of claim 19 , wherein in the second operation mode the on-times are modulated by the input instantaneous voltage to keep a product of a squared duty ratio and a cycle time in the second operation mode to be constant and proportional to output power.
21. The controller of claim 20 , wherein in the first operation mode the on-times and the off-times are fixed so that a product of a squared duty ratio and a cycle time in the first operation mode is constant and equal to the product in the second operation mode.
22. The controller of claim 18 , wherein the third operation mode controls the switch such that the power converter is operated in discontinuous conduction mode with the on-times and the off-times fixed.
23. The controller of claim 22 , wherein the on-times and the off-times in the third operation mode are fixed and determined by pulse frequency modulation.
24. The controller of claim 18 , further comprising a feedback signal generator for generating an analog feedback signal representing an output voltage of the power converter, the feedback signal generator including:
a first comparator for comparing a voltage sensed at an auxiliary winding of a transformer in the power stage with a constant zero voltage switching reference voltage to generate a first comparator output signal;
a second comparator for comparing the voltage sensed at the auxiliary winding of the transformer in the power stage with the analog feedback signal to generate a second comparator output signal;
a sampling module for determining delta differences between high and low edges of the first comparator output signal and the second comparator output signal;
a summation module for summing the delta differences to generate a digital feedback signal; and
a digital-to-analog converter for converting the digital feedback signal to the analog feedback signal.
25. The controller of claim 18 , wherein the current waveform synthesizer module includes:
an adder for adding a control voltage indicating a difference between an output feedback voltage and a reference feedback voltage to a feed-forward voltage indicating a squared value of an average input voltage;
an on-time slope generator for generating an on-time ramp signal using an output of the adder;
a first comparator for comparing the on-time ramp signal with a reference voltage to generate on-times for the switch;
an off-time slope generator for generating an off-time ramp signal using the control voltage; and
a second comparator for comparing the off-time ramp signal with an off-time reference voltage to generate off-times for the switch.
26. The controller of claim 18 , wherein the current waveform synthesizer module includes:
a multiplier for multiplying a control voltage indicating a difference between an output feedback voltage and a reference feedback voltage to a reference voltage;
an on-time slope generator for generating an on-time ramp signal based upon a feed-forward voltage indicating a squared value of an average input voltage;
a first comparator for comparing the on-time ramp signal with an output of the multiplier to generate on-times for the switch;
an off-time slope generator for generating an off-time ramp signal based upon the control voltage; and
a second comparator for comparing the off-time ramp signal with an off-time reference voltage to generate off-times for the switch.
27. A power converter comprising:
transferring means for transferring electrical power from a power source to a load;
switching means in the transferring means that electrically couples or decouples the load to or from the power source; and
controlling means coupled to the switching means for shaping input current to the power converter based on a reference waveform shape, the controlling means comprising:
current shaping means for determining waveform synthesis parameters based upon an input voltage signal and the reference waveform shape;
operation mode selection means for selecting one of a plurality of operation modes for controlling on-times and off-times of a switch in the power converter, the operation modes including a first operation mode selected if an input voltage to the power converter is in a first input voltage range, a second operation mode selected if the input voltage to the power converter is in a second input voltage range, and a third operation mode selected if an output current from the power converter is lower than a predetermined threshold current or if the on-times are lower than a predetermined threshold on-time; and
current waveform synthesis means for synthesizing the input current waveform in real time by controlling on-times and off-times of the switch based upon the determined waveform synthesis parameters and the selected operation modes.