Multi-mode control based series-resonant DC-DC power converter
View Patent ↗A bi-directional series-resonant DC-DC power converter apparatus incorporating an improved multi-mode controller eliminates burst mode operation while supporting a wide voltage range handling capability. The converter includes a half bridge switching network and a full bridge switching network coupled together with a series resonant impedance including an inductor, a capacitor, and a transformer. Under normal and heavy load conditions, a controller regulates the converter output by varying the switching frequency of a half bridge and a full bridge switching network. The converter phase shift ensures ZVS operation based on a converter gain. Under light loading, the switching frequency will exceed a pre-determined maximum frequency and a second control mode is employed where the switching frequency is set to the maximum frequency and converter output is regulated by using a feedback control loop to vary the phase shift and duty cycle of the two switching networks.
1 . An apparatus, comprising:
a series resonant circuit, the series resonant circuit comprising a series connected inductor, capacitor, and a primary winding of a transformer;
a half bridge switching circuit coupled between the series resonant circuit and a first DC voltage;
a full bridge switching circuit coupled between a secondary winding of the transformer and a second DC voltage; and
a controller configured to:
receive the first DC voltage, the second DC voltage, and produce switch control signals, wherein the switch control signals are configured to operate a first switching network and a second switching network to transfer power between the first DC voltage and the second DC voltage,
subtract a controlled voltage from a reference voltage to produce an error signal, wherein the controlled voltage is one of the first DC voltage and the second DC voltage;
apply a control algorithm to the error signal to produce a control signal;
generate a control frequency, a control duty cycle, and a control phase shift, based on the control signal; and
generate the switch control signals based on a switching frequency, a converter phase shift, and a converter duty cycle,
wherein when the control frequency is greater than a predetermined maximum switching frequency the controller is further configured to:
set the switching frequency equal to the maximum switching frequency;
set the converter phase shift to the control phase shift; and
set the converter duty cycle to the control duty cycle.
2 . The apparatus according to claim 1 , wherein the controller duty cycle is less than fifty percent.
3 . The apparatus according to claim 1 , wherein,
when power is flowing from the first DC voltage to the second DC voltage, the controlled voltage is set equal to the second DC voltage, and
when power is flowing from the second DC voltage to the first DC voltage, the controlled voltage is set equal to the first DC voltage and the converter phase shift is inverted.
4 . The apparatus according to claim 1 , wherein the control algorithm comprises a proportional plus integral control algorithm.
5 . The apparatus according to claim 1 , wherein the controller is configured to generate the control frequency, the control duty cycle, and the control phase shift by applying one or more linear functions to the control signal.
6 . The apparatus according to claim 1 , wherein the controller is configured to determine a control algorithm gain based on a comparison between the control frequency and the maximum switching frequency.
7 . The apparatus according to claim 1 , wherein the controller is configured to generate a converter gain based on the first DC voltage, the second DC voltage, and a turns ratio of the transformer, and, when the control frequency is less than the maximum switching frequency:
set the switching frequency equal to the control frequency;
set the converter duty cycle to fifty percent; and
generate the converter phase shift based on the converter gain.
8 . The apparatus according to claim 7 , wherein when the converter gain (M) is less than a predetermined maximum gain, the converter phase shift is set to an inverse cosine of the converter gain.
9 . The apparatus according to claim 8 , wherein the maximum gain is determined based on a deadtime of a high voltage switching network, a charge stored in an output capacitance of a high voltage side switch, and a minimum low voltage side output current necessary to provide zero voltage switching.
10 . A method, comprising:
a series resonant circuit, the series resonant circuit comprising a series connected inductor, capacitor, and a primary winding of a transformer;
a half bridge switching circuit coupled between the series resonant circuit and a first DC voltage; and
a full bridge switching circuit coupled between a secondary winding of the transformer and a second DC voltage;
wherein the method further comprises:
generating an error signal by subtracting a controlled voltage from a reference voltage, wherein the controlled voltage is one of the first DC voltage, and the second DC voltage;
generating a control signal by applying a control algorithm to the error signal;
generating a control frequency, a control duty cycle, and a control phase shift, based on the control signal; and
comparing the control frequency to a predetermined maximum switching frequency,
when the control frequency is greater than the predetermined maximum switching frequency, the method further comprises:
setting a converter switching frequency equal to the maximum switching frequency;
setting a converter phase shift to the control phase shift;
setting a converter duty cycle to the control duty cycle; and
generating switch control signals based on the switching frequency, the converter phase shift, and the converter duty cycle,
wherein the switch control signals are configured to operate a first switching network and a second switching network to transfer power between the first DC voltage and the second DC voltage.
11 . The method according to claim 10 , wherein the duty cycle is less than fifty percent.
12 . The method according to claim 10 , further comprising:
when power is flowing from the first DC voltage to the second DC voltage, the method further comprises setting the controlled voltage equal to the second DC voltage, and
when power is flowing from the second DC voltage to the first DC voltage, the method further comprises setting the controlled voltage to the first DC voltage, and inverting the converter phase shift.
13 . The method according to claim 10 , wherein the control algorithm comprises a proportional plus integral control algorithm.
14 . The method according to claim 10 , wherein the control frequency, the control duty cycle, and the control phase shift are generated by applying one or more linear functions to the control signal.
15 . The method according to claim 10 , wherein the control algorithm comprises a control algorithm gain, and the method further comprises determining the control algorithm gain based on a comparison between the control frequency and the maximum switching frequency.
16 . The method according to claim 10 , wherein when the control frequency is less than the predetermined maximum switching frequency, the method further comprises:
setting the switching frequency equal to the control frequency;
setting the converter duty cycle to fifty percent;
generating a converter gain based on the first DC voltage, the second DC voltage, and a turns ratio of the transformer; and
generating the converter phase shift based on the converter gain.
17 . The method according to claim 16 , further comprising:
determining a maximum gain based on a deadtime of a high voltage switching network, a charge stored in an output capacitance of a high voltage side switch, and a minimum low voltage side output current necessary to provide zero voltage switching; and
when the converter gain is less than the maximum gain, generating the converter phase shift based on an inverse cosine of the converter gain.
18 . The method according to claim 17 , wherein the maximum gain is determined based on a deadtime of the high voltage switching network, a charge stored in an output capacitance of a high voltage side switch and a minimum low voltage side output current necessary to provide zero voltage switching.