Solar photovoltaic power conditioning units
A power conditioning unit for delivering power from a dc power source to an ac mains power supply output includes a dc power input to receive dc power from a dc power source, an ac power output for delivering ac power to the ac mains power supply, a dc link coupled between the dc power input and the ac power output, first and second dc-to-dc converters coupled between the dc power input and the dc link, wherein one or both of the first and second dc-to-dc converters comprises a pair of resonant capacitors, a sensing element connected in parallel to one of the pair of the resonant capacitors for sensing a ripple voltage, and a controller operative to control the first and second dc-to-dc converters in response to the sensed ripple voltage.
1. A power conditioning unit for delivering power from a dc power source to an ac mains power supply output, the power conditioning unit comprising:
a dc power input to receive dc power from a dc power source;
an ac power output for delivering ac power to the ac mains power supply;
a dc link coupled between the dc power input and the ac power output;
first and second dc-to-dc converters coupled between the dc power input and the dc link, wherein one or both of the first and second dc-to-dc converters comprises a pair of resonant capacitors;
a sensing element connected in parallel to one of the pair of the resonant capacitors for sensing a ripple voltage; and
a controller operative to control the first and second dc-to-dc converters in response to the sensed ripple voltage.
2. The power conditioning unit of claim 1 , wherein the first and second dc-to-dc converters each comprise a plurality of rectifiers, and a transformer having a primary winding, a secondary winding including a winding tap, and an output inductor winding connected between the winding tap and the plurality of rectifiers.
3. The power conditioning unit of claim 2 , wherein the winding tap is between first and second portions of the secondary winding, wherein the first and second portions of the secondary winding of the transformer are windings on respective first and second legs of a core the transformer, and wherein the output inductor wiring is on a third leg between the first and second legs of the core of the transformer.
4. The power conditioning unit of claim 3 , wherein the output inductor winding further comprises windings on the first and second legs of the core, each wound in an opposite sense to a sense of windings of the primary winding.
5. The power conditioning unit of claim 1 , wherein the sensing element is configured to rectify the ripple voltage across one of the pair of the resonant capacitors to provide a rectified signal to the controller.
6. The power conditioning unit of claim 5 , wherein the ripple voltage has a ripple level indicative of an available power of the PV dc power source.
7. The power conditioning unit of claim 6 , further comprising an analog-to-digital converter connected to the sensing element and configured to provide a digital signal representative of the ripple voltage to the controller.
8. The power conditioning unit of claim 1 , wherein each of the first and second dc-to-dc converters comprises an input dc-to-ac converter that has a set of power switching devices to switch the dc power to the primary winding of the transformer, the power conditioning unit further comprising at least one switching controller to control the set of power switching devices such that switching is synchronized between the input dc-to-ac converters.
9. The power conditioning unit of claim 8 , wherein the switching is synchronized such that a phase angle between switching of the corresponding set of power switching devices in the input dc-to-ac converters is substantially 90 degrees or 180 degrees.
10. The power condition unit of claim 8 , wherein the controller is configured to switch off one of the dc-to-dc converters by gradually reducing the dc power fed to the dc link by the dc-to-dc converter.
11. The power conditioning unit of claim 8 , wherein the controller is configured to switch off one of the dc-to-dc converters by controlling a duty cycle of a pulse width modulated waveform of at least one of the set of power switching devices.
12. The power conditioning unit of claim 10 , wherein the controller is configured to switch off one of the dc-to-dc converters by controlling a switching frequency of at least one of the set of power switching devices to gradually move the switching frequency away from a resonant frequency of the dc-to-dc converter.
13. The power conditioning unit of claim 1 , further comprising:
a plurality of rectifiers; and
a transformer having a first primary winding connected to the first dc-to-dc converter, a second primary winding connected to the second dc-to-dc converter, a secondary winding including a winding tap, and an output inductor winding connected between the winding tap and the plurality of rectifiers.
14. The power conditioning unit of claim 13 , wherein each of the first and second dc-to-dc converters comprises an input dc-to-ac converter that has a set of power switching devices to switch the dc power to the primary winding of the transformer, the power conditioning unit further comprising at least one switching controller to control the set of power switching devices such that switching is synchronized between the input dc-to-ac converters.
15. The power conditioning unit of claim 14 , wherein the switching is synchronized such that a phase angle between switching of the corresponding set of power switching devices in the input dc-to-ac converters is substantially 90 degrees.
16. A power conditioning unit for delivering power from a dc power source to an ac mains power supply output, the power conditioning unit comprising:
a dc power input to receive dc power from a dc power source;
an ac power output for delivering ac power to the ac mains power supply;
a dc link coupled between the dc power input and the ac power output;
first and second dc-to-dc converters coupled between the dc power input and the dc link, each of the first and second dc-to-dc converters comprising a plurality of rectifiers and a transformer having a primary winding, a secondary winding including a winding tap, an output inductor winding connected between the winding tap and the plurality of rectifiers.
17. The power conditioning unit of claim 16 , wherein one of the first and second dc-to-dc converters comprises a pair of resonant capacitors, and the power conditioning unit further comprising:
a sensing element connected in parallel to one of the pair of resonant capacitors for sensing a ripple voltage; and
a controller operative to control the first and second dc-to-dc converters in response to the ripple voltage.
18. The power conditioning unit of claim 16 , wherein each of the first and second dc-to-dc converters comprises an input dc-to-ac converter that has a set of power switching devices to switch the dc power to the primary winding of the transformer, the power conditioning unit further comprising at least one switching controller to control the set of power switching devices such that switching is synchronized between the input dc-to-ac converters.
19. The power conditioning unit of claim 18 , wherein the controller is configured to switch off one of the dc-to-dc converters by gradually reducing the dc power fed to the dc link by the dc-to-dc converter.
20. The power conditioning unit of claim 18 , wherein the controller is configured to switch off one of the dc-to-dc converters by controlling a duty cycle of a pulse width modulated waveform of at least one of the set of power switching devices or by controlling a switching frequency of at least one of the set of power switching devices to gradually move the switching frequency away from a resonant frequency of the dc-to-dc converter.