Power conversion circuit with switching modes, and control method thereof
A power conversion circuit includes a switching circuit, a resonant circuit, a rectifying circuit, a controller and a transformer including a primary winding and a secondary winding. The resonant circuit is electrically coupled to the switching circuit and the primary winding. The rectifying circuit is electrically coupled to the secondary winding. The controller is electrically coupled to the switching circuit and the rectifying circuit and configured to selectively output one of a frequency modulation signal and a pulse width modulation signal as a second control signal according to a working frequency of a first control signal.
1. A power conversion circuit, comprising:
a switching circuit;
a resonant circuit electrically coupled to the switching circuit;
a transformer comprising:
a primary winding electrically coupled to the resonant circuit; and
a secondary winding;
a rectifying circuit electrically coupled to the secondary winding of the transformer; and
a controller electrically coupled to the switching circuit and the rectifying circuit, and configured to selectively output one of a frequency modulation signal and a pulse width modulation signal as a second control signal according to a working frequency of a first control signal to control the switching circuit,
wherein the controller is configured to control a duty cycle of the second control signal on the condition that the working frequency is higher than a setting frequency.
2. The power conversion circuit of claim 1 , wherein the controller is configured to control a switching frequency of the second control signal on the condition that the working frequency is lower than the setting frequency.
3. The power conversion circuit of claim 1 , wherein the controller is further configured to detect an output voltage of the rectifying circuit, obtain a frequency command according to the difference between the output voltage and a reference voltage, and output the first control signal according to the frequency command.
4. The power conversion circuit of claim 3 , wherein the controller is further configured to detect an output current of the rectifying circuit, and adjust the frequency command by a frequency compensation value according to the output current.
5. The power conversion circuit of claim 4 , wherein the controller is further configured to determine the load according to the variation of the output current to adjust a current gain value, and adjust the frequency compensation value according to the current gain value.
6. The power conversion circuit of claim 4 , wherein the controller is configured to adjust the frequency compensation value according to a first current gain value on the condition that the controller determines that the load is increased, and adjust the frequency compensation value according to a second current gain value on the condition that the controller determines that the load is decreased, wherein the second current gain value is larger than the first current gain value.
7. The power conversion circuit of claim 4 , wherein the controller is configured to reduce the frequency command according to the frequency compensation value on the condition that the variation of the output current is larger than zero.
8. The power conversion circuit of claim 4 , wherein the controller is further configured to determine whether the variation of the frequency compensation value is larger than a variation threshold on the condition that the variation of the output current is smaller than zero, and set the frequency compensation value to be zero if the variation of the frequency compensation value is larger than the variation threshold.
9. The power conversion circuit of claim 4 , wherein the controller is further configured to determine whether the variation of the frequency compensation value is larger than a variation threshold on the condition that the variation of the output current is smaller than zero, and determine the frequency compensation value corresponding to the working frequency based on a characteristic curve if the variation of the frequency compensation value is smaller than or equal to the variation threshold.
10. The power conversion circuit of claim 1 , further comprising:
an isolated driver electrically coupled between the controller and the switching circuit, and configured to feedback to drive the switching circuit.
11. A control method of a power conversion circuit, comprising:
detecting, by the controller, an output voltage and an output current of a rectifying circuit of the power conversion circuit;
obtaining, by the controller, a frequency command according to the difference between the output voltage and a reference voltage;
adjusting, by the controller, the frequency command by a frequency compensation value according to the output current;
outputting, by a controller, a second control signal according to the frequency command; and
converting, by a switching circuit of the power conversion circuit, a DC input voltage into a switching signal according to the second control signal.
12. The control method of the power conversion circuit of claim 11 , further comprising:
controlling, by the controller, a switching frequency of the second control signal on the condition that a working frequency of the frequency command is smaller than a setting frequency; and
controlling, by the controller, a duty cycle of the second control signal on the condition that the working frequency is larger than the setting frequency.
13. The control method of the power conversion circuit control method of claim 11 , further comprising:
determining, by the controller, the load according to the variation of the output current to adjust a current gain value; and
adjusting, by the controller, the frequency command according to the current gain value.
14. The control method of the power conversion circuit of claim 13 , wherein the operation of determining the load to adjust the current gain value according to the variation of the output current comprises:
adjusting, by the controller, the frequency compensation value according to a first current gain value if the controller determines that the load is increased; and
adjusting, by the controller, the frequency compensation value according to a second current gain value if the controller determines that the load is decreased, wherein the second current gain value is larger than the first current gain value.
15. The control method of the power conversion circuit of claim 13 , wherein the operation of determining the load to adjust the current gain value according to the variation of the output current comprises:
reducing, by the controller, the frequency command according to the frequency compensation value if the variation of the output current is larger than zero.
16. The control method of the power conversion circuit of claim 13 , wherein the operation of determining the load to adjust the current gain value according to the variation of the output current comprises:
determining, by the controller, whether the variation of the frequency compensation value is larger than a variation threshold if the variation of the output current is smaller than zero; and
setting, by the controller, the frequency compensation value to be zero if the variation of the frequency compensation value is larger than the variation threshold.
17. The control method of the power conversion circuit of claim 13 , wherein the operation of determining the load to adjust the current gain value according to the variation of the output current comprises:
determining, by the controller, whether the variation of the frequency compensation value is larger than a variation threshold if the variation of the output current is smaller than zero; and
determining, by the controller, the frequency compensation value corresponding to the working frequency based on a characteristic curve if the variation of the frequency compensation value is smaller than or equal to the variation threshold.
18. The control method of the power conversion circuit of claim 11 , further comprising:
receiving, by an isolated driver, the second control signal of the controller and feeding back a driving signal to drive the switching circuit.