LLC resonant converter and control method therefor
A control method for an LLC resonant converter includes: dividing an input voltage into four voltage segments: a low voltage, a medium-low voltage, a medium-high voltage, and a high voltage, and correspondingly adopting a full-bridge PFM control mode, a full-bridge PWM control mode, a half-bridge PFM control mode, and a half-bridge PWM control mode respectively. This control method is applicable to a wide input voltage range to achieve steady-state control over an LLC resonant converter, and can maintain a high efficiency of the LLC resonant converter within the whole input voltage range and can also be used in scenarios where a wide output voltage occurs.
1 . A control method for an LLC resonant converter, wherein the LLC resonant converter has an inverter circuit, an LLC resonant circuit, a transformer, and a secondary-side rectifier filter circuit, the inverter circuit has a power transistor Q 1 , a power transistor Q 2 , a power transistor Q 3 , and a power transistor Q 4 , the drain electrode of the power transistor Q 1 is connected to the drain electrode of the power transistor Q 3 and a positive terminal of an input voltage, the source electrode of the power transistor Q 1 is connected to the drain electrode of the power transistor Q 2 , the source electrode of the power transistor Q 3 is connected to the drain electrode of the power transistor Q 4 , the source electrode of the power transistor Q 2 and the source electrode of the power transistor Q 4 are respectively connected to a negative terminal of the input voltage, and the control method comprises:
dividing a range of an output voltage of the secondary-side rectifier filter circuit into a low voltage range, a medium-low voltage range, a medium-high voltage range, and a high voltage range; and
correspondingly adopting different control modes for the LLC resonant converter in the low voltage range, the medium-low voltage range, the medium-high voltage range, and the high voltage range respectively; wherein
when the output voltage is in the low voltage range, adopting a half-bridge PWM control mode for the LLC resonant converter;
when the output voltage is in the medium-low voltage range, adopting a half-bridge PFM control mode for the LLC resonant converter;
when the output voltage is in the medium-high voltage range, adopting a full-bridge PWM control mode for the LLC resonant converter; and
when the output voltage is in the high voltage range, adopting a full-bridge PFM control mode for the LLC resonant converter.
2 . The control method for an LLC resonant converter according to claim 1 , wherein
the LLC resonant circuit has a resonant inductor, an excitation inductor, a capacitor, a power transistor Q 5 , and a power transistor Q 6 , the drain electrode of the power transistor Q 5 is connected to one end of the capacitor, the source electrode of the power transistor Q 5 is connected to the source electrode of the power transistor Q 6 , and the drain electrode of the power transistor Q 6 is connected to the source electrode of the power transistor Q 3 ;
when the LLC resonant converter operates in the half-bridge PWM control mode, a frequency and a duty cycle of a driving signal of the power transistor Q 2 are respectively the same as those of the driving signal of the power transistor Q 1 , a phase difference between the driving signal of the power transistor Q 2 and the driving signal of the power transistor Q 1 is 180°, the power transistor Q 3 is continuously turned off, the power transistor Q 4 is continuously turned on, a driving signal of the power transistor Q 5 is complementary to that of the power transistor Q 1 , and a driving signal of the power transistor Q 6 is complementary to that of the power transistor Q 2 ;
when the LLC resonant converter operates in the half-bridge PFM control mode, a duty cycle of a driving signal of the power transistor Q 1 is 50%, a frequency and a duty cycle of a driving signal of the power transistor Q 2 are respectively the same as those of the driving signal of the power transistor Q 1 , a phase difference between the driving signal of the power transistor Q 2 and the driving signal of the power transistor Q 1 is 180°, the power transistor Q 3 is continuously turned off, the power transistor Q 4 is continuously turned on, the power transistor Q 5 is continuously turned off, and the power transistor Q 6 is continuously turned off;
when the LLC resonant converter operates in the full-bridge PWM control mode, a frequency and a duty cycle of a driving signal of the power transistor Q 2 are respectively the same as those of the driving signal of the power transistor Q 1 , a phase difference between the driving signal of the power transistor Q 2 and the driving signal of the power transistor Q 1 is 180°, a driving signal of the power transistor Q 3 is the same as that of the power transistor Q 2 , and a driving signal of the power transistor Q 4 is the same as that of the power transistor Q 1 , a driving signal of the power transistor Q 5 is complementary to that of the power transistor Q 1 , and a driving signal of the power transistor Q 6 is complementary to that of the power transistor Q 2 ; and
when the LLC resonant converter operates in the full-bridge PFM control mode, a duty cycle of a driving signal of the power transistor Q 1 is 50%, a frequency and a duty cycle of a driving signal of the power transistor Q 2 are respectively the same as those of the driving signal of the power transistor Q 1 , a phase difference between the driving signal of the power transistor Q 2 and the driving signal of the power transistor Q 1 is 180°, a driving signal of the power transistor Q 3 is the same as that of the power transistor Q 2 , a driving signal of the power transistor Q 4 is the same as that of the power transistor Q 1 , the power transistor Q 5 is continuously turned off, and the power transistor Q 6 is continuously turned off.
3 . The control method for an LLC resonant converter according to claim 1 , wherein the secondary-side rectifier filter circuit is a full-wave rectifier circuit or a full-bridge rectifier circuit.
4 . The control method for an LLC resonant converter according to claim 1 , wherein the control method is used in a unidirectional LLC resonant converter.
5 . An LLC resonant converter, configured to convert an input voltage into an output voltage, wherein
when the output voltage is in a low voltage range, the LLC resonant converter is configured to operate in a half-bridge PWM control mode;
when the output voltage is in a medium-low voltage range, the LLC resonant converter is configured to operate in a half-bridge PFM control mode;
when the output voltage is in a medium-high voltage range, the LLC resonant converter is configured to operate in a full-bridge PWM control mode; and
when the output voltage is in a high voltage range, the LLC resonant converter is configured to operate in a full-bridge PFM control mode.
6 . The LLC resonant converter according to claim 5 , wherein
the LLC resonant converter has an inverter circuit, an LLC resonant circuit, a transformer, and a secondary-side rectifier filter circuit,
the inverter circuit has a power transistor Q 1 , a power transistor Q 2 , a power transistor Q 3 , and a power transistor Q 4 , the drain electrode of the power transistor Q 1 is connected to the drain electrode of the power transistor Q 3 and a positive terminal of an input voltage, the source electrode of the power transistor Q 1 is connected to the drain electrode of the power transistor Q 2 , the source electrode of the power transistor Q 3 is connected to the drain electrode of the power transistor Q 4 , the source electrode of the power transistor Q 2 and the source electrode of the power transistor Q 4 are respectively connected to a negative terminal of the input voltage,
the LLC resonant circuit has a resonant inductor, an excitation inductor, a capacitor, a power transistor Q 5 , and a power transistor Q 6 , the drain electrode of the power transistor Q 5 is connected to one end of the capacitor, the source electrode of the power transistor Q 5 is connected to the source electrode of the power transistor Q 6 , and the drain electrode of the power transistor Q 6 is connected to the source electrode of the power transistor Q 3 .