Adaptive control of resonant power converters
A power converter including a transformer, a resonant circuit including the transformer and a resonant capacitor having a characteristic resonant frequency and period, and output circuitry connected to the transformer for delivering a rectified output voltage to a load. Primary switches drive the resonant circuit, a switch controller operates the primary switches in a series of converter operating cycles which include power transfer intervals of adjustable duration during which a resonant current at the characteristic resonant frequency flows through a winding of the transformer. The operating cycles may also include energy recycling intervals of variable duration for charging and discharging capacitances within the converter. A gate driver includes a transformer, a plurality of switches, a current monitor, and a controller that operates the switches in a series of driver operating cycles having adjustable ON periods and adjustable transition periods during which capacitances are resonantly charged and discharged.
1. An apparatus comprising a converter for converting power from a source at a source voltage, V S , for delivery to a load at a rectified output voltage, V OUT , where a current drawn by the load, I L , may vary over a normal operating range from a minimum load current, I L-MAX , to a maximum load current, I L-MAX , the converter comprising:
a resonant circuit comprising a transformer having a characteristic resonant frequency and a characteristic resonant period;
output circuitry connected to the transformer configured to deliver the rectified output voltage to the load;
input circuitry including two or more primary switches configured to drive the resonant circuit; and
a switch controller designed and configured to operate the two or more primary switches in a series of converter operating cycles to provide an essentially fixed voltage transformation ratio, K=V OUT /V IN , at a load current, wherein each converter operating cycle is characterized by (a) two power transfer intervals of essentially equal duration, each interval having a duration, T PTI , less than the characteristic resonant period, during which one or more of the two or more primary switches are ON, a resonant current at the characteristic resonant frequency and a magnetizing current flowing through a winding of the transformer, and power is transferred from an input of the converter to an output of the converter via the transformer; and (b) two energy-recycling intervals, each having a duration during which the two or more primary switches are OFF and currents in the converter are used to charge and discharge capacitances in the converter;
wherein the switch controller is configured to adjust the duration of each power transfer interval, T PTI , of the two power transfer intervals from a predetermined full duration, T PTI-FULL , to a predetermined minimum duration, T PTI-MIN , as a function of variations in the load current, I L , between a first predetermined threshold, I L1 , and a second predetermined threshold, I L2 ;
wherein the predetermined full duration, T PTI-FULL , is established to be approximately equal one half of the characteristic resonant period, for each power transfer interval for conditions in which the load current, I L , is greater than or equal to the first predetermined threshold, I L1 .
2. The apparatus of claim 1 ,
wherein the predetermined minimum duration, T PTI-MIN , is established for each power transfer interval for conditions in which the load current, I L , is less than or equal to the second predetermined threshold, I L2 .
3. The apparatus of claim 2 , wherein the switch controller is configured to adjust the duration of each energy recycling interval, T ERI , to vary from a maximum duration, T ERI-MAX , at times when the duration of the power transfer interval is set to the predetermined minimum duration, T PTI-MIN , and to a minimum duration, T ERI-MIN , at times when the duration of the power transfer interval is set to the predetermined maximum duration, T PT-MAX .
4. The apparatus of claim 2 , wherein the first predetermined threshold, I L1 , is greater than or equal to 33 percent of the maximum load current, I L-MAX .
5. The apparatus of claim 2 , wherein the first predetermined threshold, I L1 , is greater than or equal to 50 percent of the maximum load current, I L-MAX .
6. The apparatus of claim 2 , wherein the first predetermined threshold, I L1 , is greater than or equal to 65 percent of the maximum load current, I L-MAX .
7. The apparatus of claim 2 , wherein the second predetermined threshold, I L2 , is approximately equal to the minimum load current, I L-MIN .
8. The apparatus of claim 7 , wherein the minimum load current, I L-MIN , is zero.
9. The apparatus of claim 2 , wherein the predetermined minimum duration, T PTI-MIN , is greater than or equal to 25 percent of the characteristic resonant period.
10. The apparatus of claim 2 , wherein the predetermined minimum duration, T PTI-MIN , is in a range between 25 to 35 percent of the characteristic resonant period.
11. The apparatus of claim 1 , wherein the switch controller is configured to turn the two or more primary switches ON at times when a voltage across the respective primary switch, V SW , of the two or more primary switches is approximately zero.
12. The apparatus of claim 1 , wherein the switch controller is configured to turn the two or more primary switches ON at times when a voltage across the respective primary switch, V SW , of the two or more primary switches is less than 25 percent of a maximum voltage across the respective primary switch, V SW-MAX , of the two or more primary switches in the OFF state during normal operation.
13. The apparatus of claim 1 , further comprising a non-isolated power train.
14. The apparatus of claim 1 , wherein the input circuitry and at least a portion of the output circuitry are connected in series across the source such that an absolute value of an input voltage V IN applied to the input circuitry is approximately equal to an absolute value of the source voltage V S minus a number N times an absolute value of the output voltage V OUT , where N is at least 1.
15. The apparatus of claim 1 , wherein the resonant circuit comprises a resonant capacitor, and
wherein the apparatus comprises a clamp switch configured to clamp the resonant capacitor; and each power transfer interval of the two power transfer intervals comprises:
(i) first and second resonant intervals, each having a duration less than one half of the characteristic resonant period, during which the resonant current flows at the characteristic resonant frequency; and
(ii) a clamp interval occurring after the first resonant interval and before the second resonant interval and having a clamp duration during which the clamp switch is ON and provides a low impedance shunt across the resonant capacitor.
16. The apparatus of claim 1 , wherein the switch controller comprises a digital controller.
17. The apparatus of claim 16 , wherein timing parameters, including the durations of the two power transfer intervals, are digitally set and adaptively reset using at least one look-up table as a function of the load.