Solar photovoltaic system with maximized ripple voltage on storage capacitor
We describe a photovoltaic (PV) power generation system comprising at least two PV panels and a power conditioning unit. The dc power outputs of the PV panels are connected in parallel to a dc power input of the power conditioning unit. The power conditioning unit comprises a dc-to-dc converter having an input coupled to the dc power input and an output coupled to a dc link of the unit, a dc-to-ac converter having an input coupled to the dc link and an ac mains power supply output, and an energy storage capacitor coupled to the dc link. The power conditioning unit is configured to perform maximum power point tracking (MPPT) responsive to a level of power flowing into the dc power input, and the level of power flowing into said dc power input is sensed at the dc link. In preferred implementations the energy storage capacitor is a non-electrolytic capacitor.
1. A method for generating a three phase ac mains power supply from a plurality of photovoltaic panels, the method comprising:
connecting dc power outputs from the plurality of photovoltaic panels in parallel to an input of a power conditioning unit; and
converting an input flow of dc power from the dc power outputs into the three phase ac mains power supply using the power conditioning unit, wherein the converting comprises converting the input flow of dc power into an intermediate flow of dc power on a dc link of the power conditioning unit coupled to an energy storage capacitor having a ripple voltage that is proportional to the intermediate flow of dc power on the dc link, and converting the intermediate flow of dc power to the three phase ac mains power supply with a dc to ac converter that is controlled to maximize the ripple voltage on the energy storage capacitor.
2. A method as claimed in claim 1 further comprising tracking substantially a maximum power point of the input flow of dc power by sensing the intermediate flow of dc power and controlling the converting of the intermediate flow of dc power to the three phase ac mains power supply responsive to the sensing.
3. A method as claimed in claim 2 wherein the sensing comprising sensing a voltage but not a current on the dc link.
4. A method as claimed in claim 2 wherein the power conditioning unit has a single, common maximum power point tracking control system that controls the input flow of dc power from the plurality of photovoltaic panels.
5. A method as claimed in claim 1 wherein the converting of the input flow of dc power into the intermediate flow of dc power comprises increasing an input voltage from the parallel connected photovoltaic panels by substantially a fixed amplification factor.
6. A method as claimed in claim 1 wherein the dc power outputs from the photovoltaic panels are connected to an input of a dc to dc converter of the power conditioning unit.
7. A method as claimed in claim 6 wherein a choke is coupled between an output of the dc to dc converter and the energy storage capacitor.
8. A method as claimed in claim 6 wherein the dc to dc converter is controlled to supply dc power to the energy storage capacitor depending on an additional amount of energy capacity available in the energy storage capacitor.
9. A method as claimed in claim 1 wherein a maximum capacitance value for the energy storage capacitor is 50 microfarads.
10. A method as claimed in claim 1 wherein the energy storage capacitor is a non-electrolytic capacitor.
11. A method as claimed in claim 1 wherein the three phase ac mains power supply comprises one dc to ac converter per phase, each coupled to the dc link.
12. A method as claimed in claim 1 wherein a power capacity for the power conditioning unit is adjusted by changing a capacitance value of the energy storage capacitor.
13. A system for generating three phase ac mains power supply from a plurality of photovoltaic panels, the system comprising:
means for connecting dc power outputs from the photovoltaic panels in parallel to an input of a power conditioning unit to provide a common flow of dc power;
means for converting an input flow of dc power from the dc power outputs into the three phase ac mains power supply using the power conditioning unit, wherein the converting comprises converting the input flow of dc power into an intermediate flow of dc power on a dc link of the power conditioning unit coupled to an energy storage capacitor having a ripple voltage that is proportional to the intermediate flow of dc power on the dc link; and
means for converting the intermediate flow of dc power to the three phase ac mains power supply with a dc to ac converter that is controlled to maximize the ripple voltage on the energy storage capacitor.
14. A photovoltaic power generation system as claimed in claim 13 wherein the power conditioning unit comprises one dc-to-ac converter per phase each coupled to the dc link.
15. A photovoltaic power generation system as claimed in claim 13 wherein the power conditioning unit has a single, common maximum power point tracking control system that controls the input flow of dc power from the plurality of photovoltaic panels.
16. A photovoltaic power generation system as claimed in claim 13 wherein the dc power outputs from the photovoltaic panels are connected to an input of a dc to dc converter of the power conditioning unit.
17. A photovoltaic power generation system as claimed in claim 16 wherein a choke is coupled between an output of the dc to dc converter and the energy storage capacitor.
18. A photovoltaic power generation system as claimed in claim 16 wherein the dc to dc converter is controlled to supply dc power to the energy storage capacitor depending on an additional amount of energy capacity available in the energy storage capacitor.
19. A photovoltaic power generation system as claimed in claim 13 wherein a maximum capacitance value for the energy storage capacitor is 50 microfarads.
20. A method as claimed in claim 13 wherein a power capacity for the power conditioning unit is adjusted by changing a capacitance value of the energy storage capacitor.
21. A photovoltaic power generation system, the system comprising:
at least two photovoltaic panels for generating dc power, each having a dc power output;
a power conditioning unit having a dc power input and a three phase ac output for delivering power to a three phase ac mains, wherein the dc power outputs of the at least two photovoltaic panels are connected in parallel to the dc power input, the power conditioning unit comprising:
a dc-to-dc converter having an input coupled to the dc power input and an output coupled to a dc link, wherein the dc-to-dc converter is configured to convert dc power received from the at least two photovoltaic panels into an intermediate flow of dc power on the dc link;
an energy storage capacitor coupled to the dc link and having a ripple voltage that is proportional to the intermediate flow of dc power on the dc link; and
a dc-to-ac converter having an input coupled to the dc link and an output coupled to the three phase ac mains, wherein the dc-to-ac converter is configured to convert the intermediate flow of dc power on the dc link to three phase ac power for delivery to the three phase ac mains, and to maximize the ripple voltage on the energy storage capacitor.