LLC resonant converter and method for suppressing ripples in output voltage thereof
The present disclosure discloses an LLC resonant converter and a method for suppressing ripples in output voltage of the LLC resonant converter. The LLC resonant converter comprises: a half-bridge or full-bridge chopper having a driving circuit, an inductance-capacitance series resonant network coupled to the chopper, an isolation transformer coupled to the resonant network, and a rectification and filtering circuit coupled to the isolation transformer; a feedforward controller coupled to generate a feedforward signal based on an input voltage; and a controlled oscillator coupled to receive the feedforward signal from the feedforward controller and to control an operating frequency of the chopper via the driving circuit based on the feedforward signal. Thus, a feedforward correction is provided for the LLC resonant converter, so that ripples in a DC output voltage of the LLC resonant converter are reduced.
1. An LLC resonant converter, comprising:
a half-bridge or full-bridge chopper having a driving circuit;
an inductance-capacitance series resonant network coupled to the chopper;
an isolation transformer coupled to the resonant network;
a rectification and filtering circuit coupled to the isolation transformer;
a linear proportional feedforward controller comprising at least one of a low-pass filter and a band-pass filter coupled to generate a feedforward signal based on an input voltage; and
a controlled oscillator coupled to receive the feedforward signal from the feedforward controller and to control an operating frequency of the chopper via the driving circuit based on the feedforward signal.
2. The LLC resonant converter according to claim 1 , further comprising:
a feedback controller coupled to generate a feedback signal based on an output error voltage of the LLC resonant converter;
wherein the controlled oscillator is coupled to receive the feedback signal and the feedforward signal to control the operating frequency of the chopper via the driving circuit.
3. The LLC resonant converter according to claim 2 , wherein the feedforward signal and the feedback signal are summed at an input side of the controlled oscillator.
4. The LLC resonant converter according to claim 2 , wherein the feedforward controller, the feedback controller and/or the controlled oscillator are implemented by an analog circuit, or by a discrete circuit that is based on an equivalent or approximate transformation.
5. The LLC resonant converter according to claim 1 , wherein the feedforward controller comprises the low-pass filter.
6. The LLC resonant converter according to claim 5 , wherein a transfer function of the low-pass filter satisfies the following equation:
G
7
(
s
)
=
Ke
·
ω
n
s
+
ω
n
where Ke represents a filter coefficient of the low-pass filter, ωn represents an ripple angular frequency, and s represents an argument of Laplace transformation.
7. The LLC resonant converter according to claim 1 , wherein the feedforward controller comprises the band-pass filter.
8. The LLC resonant converter according to claim 7 , wherein a transfer function of the band-pass filter satisfies the following equation:
G
7
(
s
)
=
Ke
·
2
·
ξ
·
ω
n
·
s
s
2
+
2
·
ξ
·
ω
n
·
s
+
ω
n
2
where Ke represents a filter coefficient of the band-pass filter, ωn represents a natural oscillation angular frequency, s represents an argument of Laplace transformation, and ξ represents a damping coefficient.
9. A method for suppressing ripples in an output voltage of an LLC resonant converter, the LLC resonant converter comprising a half-bridge or full-bridge chopper having a driving circuit, an inductance-capacitance series resonant network coupled to the chopper, an isolation transformer coupled to the resonant network, and a rectification and filtering circuit coupled to the isolation transformer, the method comprising:
generating, by a linear proportional feedforward controller comprising at least one of a low-pass filter and a band-pass filter, a feedforward signal based on an input voltage; and
controlling, by a controlled oscillator, an operating frequency of the chopper based on the feedforward signal.
10. The method according to claim 9 , wherein the filter has a band-pass filtering characteristic.
11. The method according to claim 10 , wherein the filter is implemented by an analog circuit, or by a discrete circuit that is based on an equivalent or approximate transformation.
12. A method for suppressing ripples in an output voltage of an LLC resonant converter, the LLC resonant converter comprising a half-bridge or full-bridge chopper having a driving circuit, an inductance-capacitance series resonant network coupled to the chopper, an isolation transformer coupled to the resonant network, and a rectification and filtering circuit coupled to the isolation transformer, the method comprising:
generating, by a linear proportional feedforward controller comprising at least one of a low-pass filter and a band-pass filter, a feedforward signal based on an input voltage;
generating a feedback signal based on an output error voltage of the LLC resonant converter;
generating a control signal by summing the feedback signal and the feedforward signal; and
controlling, by a controlled oscillator, an operating frequency of the chopper based on the control signal.
13. The method according to claim 12 , wherein the filter has a low-pass filtering characteristic.
14. The method according to claim 13 , wherein the filter is implemented by an analog circuit, or by a discrete circuit that is based on an equivalent or approximate transformation.