Control of a multiple input solar power inverter
View Patent ↗A solar power inverter includes a number of photovoltaic (PV) inputs for connecting PV modules, a DC-DC converter at each of the PV inputs and a DC-AC inverter for converting the outputs of the DC-DC converters to an AC output power that may be fed into a power grid. The invention provides a method of controlling such a solar power inverter including the steps of identifying a PV input by assigning a priority value to the PV inputs and identifying the PV input with the highest assigned priority value, calculating a set value for the DC-DC converter at the identified PV input that is equal or below a maximum power capacity of the PV module connected to the identified PV input, and applying the set value for the DC-DC converter at the identified PV input.
1. A method of controlling a solar power inverter having two or more photovoltaic inputs for connecting photovoltaic modules, a DC-DC converter at each of the photovoltaic inputs and a DC-AC inverter for converting the outputs of the DC-DC converters to an AC output power to be outputted at an output of the solar power inverter, the method including the steps of calculating and applying a set value for an input power of the DC-DC converter at one of the photovoltaic inputs, characterised by the steps of
identifying a photovoltaic input by assigning a priority value to at least a part of the photovoltaic inputs and identifying the photovoltaic input with the highest assigned priority value,
calculating the set value for the DC-DC converter at the identified photovoltaic input to be equal or below a maximum power capacity of the photovoltaic module connected to the identified photovoltaic input
and applying the set value for the DC-DC converter at the identified photovoltaic input,
wherein the priority values are assigned to the photovoltaic inputs in two or more stages such that in each stage the priority values of two photovoltaic inputs are compared and the photovoltaic input with the higher priority is chosen to be the identified PV input or advances to the next stage to be compared with one of the remaining photovoltaic inputs.
2. The method according to claim 1 , wherein assigning a priority value to at least a part of the photovoltaic inputs includes a step of obtaining a module value representative of a characteristic of the respective photovoltaic module connected to said photovoltaic inputs and determining the priority value under consideration of the obtained module values.
3. The method according to claim 2 , wherein an output voltage of the photovoltaic modules is measured and wherein a priority value is assigned to the PV inputs each PV module such that a PV module having a lower output voltage is assigned a higher priority value than a PV module having a higher output voltage.
4. The method according to claim 2 , wherein a temperature of the PV inputs is measured and wherein a priority value is assigned to each PV module such that a PV module connected to a PV input having a higher temperature is assigned a higher priority value than a PV module connected to a PV input having a lower temperature.
5. The method according to claim 2 , wherein a run-time of all PV modules connected to the PV inputs is acquired and wherein a priority value is assigned to each PV module such that a PV module having a longer run-time is assigned a higher priority value than a PV module having a shorter run-time.
6. The method according to claim 1 , herein the set value is calculated and applied repeatedly.
7. The method according to claim 1 wherein two or more photovoltaic inputs are identified and a set value for the input power of the DC-DC converters connected to the identified photovoltaic inputs are calculated and applied in an order of their priority values.
8. The method according to claim 1 , wherein the set value for the input power of all DC-DC converters are set such that a sum of these input powers is equal to or below a maximum output power of the solar power inverter.
9. The method according to claim 1 , wherein during a transition from one identified photovoltaic input to another identified photovoltaic input, a power of the solar power inverter is allowed to exceed a maximum output power of the solar power inverter.
10. The method according to claim 9 , wherein the power of the solar power inverter may exceed the maximum output power of the solar power inverter by a defined percentage of the maximum output power, where the defined percentage is less than 3%.
11. The method according to claim 1 , wherein, after a change from one photovoltaic input to another photovoltaic input, the input power of at least one of the photovoltaic inputs is increased to a maximum photovoltaic input power.
12. The method according to claim 1 , wherein the set value for the DC-DC converter at the identified photovoltaic input number N at step n is designated as P PVN[n] and calculated according to the following formula
P PVN [ n ]=MIN{ P PVN [ n ], P max −SUM( P PVXin )}
where P max is the maximum photovoltaic input power of the solar power inverter and SUM(P PVXin ) is a sum of the measured photovoltaic input powers of all photovoltaic modules connected to the remaining PV inputs.
13. A solar power inverter having two or more photovoltaic inputs, a DC-DC converter at each of the photovoltaic inputs and a DC-AC inverter for converting the outputs of the DC-DC converters to an AC output power to be outputted at an output of the solar power inverter, characterised in that the solar power inverter includes a control device for calculating and applying a set value for an input power of the DC-DC converter at one of the photovoltaic inputs, wherein the control device is further adapted to
identify a photovoltaic input by assigning a priority value to at least a part of the photovoltaic inputs and identifying the photovoltaic input with the highest assigned priority value,
calculate the set value for the DC-DC converter at the identified photovoltaic input to be equal or below a maximum power capacity of a photovoltaic module connected to the identified photovoltaic input
and applying the set value to the DC-DC converter at the identified photovoltaic input
wherein the control device is further adapted to assign the priority values to the photovoltaic inputs in two or more stages such that in each stage the priority values of two photovoltaic inputs are compared and the photovoltaic input with the higher priority is chosen to be the identified PV input or advances to the next stage to be compared with one of the remaining photovoltaic inputs.
14. The method according to claim 6 , wherein the set value is calculated and applied in regular time intervals between 5 seconds and 10 minutes.
15. The method according to claim 10 , wherein the defined percentage is 1% or less.
16. The method according to claim 11 , wherein the input power of at least one of the photovoltaic inputs is increased to a maximum photovoltaic input power in regular steps of 1% of a maximum photovoltaic input power P PVNmax of PV input number N according to the following formula
P PVN [ n ]=MIN{ P PVNmax ,P PVN [ n− 1]+( P PVNmax *1%)}
where P PVN[n] is the calculated set value for the input power at the PV input Number N at step n and P PVN[n] is the calculated set value for the input power at the PV input number N at step n−1.