Regulation of contribution of secondary energy sources to power grid
An energy storage medium is combined with a secondary energy source that supplies power to an electricity distribution grid. The charge and discharge behavior of the energy storage medium is controlled so that rapid increases in the output of a secondary source of energy are absorbed by the storage system, whereas rapid decreases in the output of the secondary source are compensated by discharging stored energy onto the grid. The combined contributions of the secondary source and the energy storage system ensures a rate of change that does not exceed a defined level. Maximum and minimum output power levels for the secondary source can be established to define a normal operating range. The charging or discharging of the energy storage system is also performed when the secondary output power level exceeds or falls below the limits of the defined range.
1. A method of regulating an output power of a source of electricity that is supplied to an electricity distribution grid, the method comprising:
determining whether:
(a) the output power of the electricity source is outside a predetermined range, and
(b) a rate of change of the output power exceeds a predefined maximum value that is a function of one or more parameters that influence an expected output of the electricity source, wherein the one or more parameters is selected from the list consisting of:
a charging constraint on charging an energy storage medium, wherein the charging constraint limits charging of the energy storage medium based on unused energy storage capacity of the energy storage medium and a maximum power rating of the energy storage medium, and
a discharging constraint on discharging the energy storage medium, wherein the discharging constraint limits discharging of the energy storage medium based on available energy storage capacity of the energy storage medium and the maximum power rating of the energy storage medium; and
in response to determining that either or both of conditions (a) and (b) is met, regulating the output power supplied to the grid by transferring energy between the energy storage medium and the electricity grid,
wherein the transferring comprises discharging or charging the energy storage medium.
2. The method of claim 1 , wherein said predetermined range is defined by a lower limit value, and wherein, in response to determining that the output power of the electricity source is less than said lower limit value, transferring energy from the energy storage medium to the electricity grid by discharging or charging the energy storage medium.
3. The method of claim 2 , further comprising constraining the amount of energy transferred from the energy storage medium to the electricity grid in accordance with the predefined maximum value for the rate of change.
4. The method of claim 3 , wherein the amount of energy transferred from the energy storage medium to the electricity grid is further constrained in accordance with the lesser of the state of charge of the energy storage medium and the maximum power rating of the energy storage medium.
5. The method of claim 2 , wherein said predetermined range is further defined by an upper limit value, and wherein, in response to determining that the output power of the electricity source is greater than said upper limit value, transferring energy from the electricity grid to the energy storage medium by charging the energy storage medium.
6. The method of claim 5 , further comprising constraining the amount of energy transferred to the energy storage medium from the electricity grid in accordance with the predefined maximum value for the rate of change.
7. The method of claim 6 , wherein the amount of energy transferred to the energy storage medium from the electricity grid is further constrained in accordance with the lesser of the unused capacity of the energy storage medium and the maximum power rating of the energy storage medium.
8. The method of claim 1 , wherein the predetermined range is a function of a temporal factor.
9. The method of claim 1 , wherein the predetermined range is a function of a geographic parameter that influences the output of the electricity source.
10. The method of claim 1 , wherein the predetermined range is a function of the state of charge of the energy storage medium.
11. The method of claim 1 , wherein the one or more parameters include a temporal factor.
12. The method of claim 1 , wherein the one or more parameters include a geographic parameter that influences the output of the electricity source.
13. The method of claim 1 , wherein the predetermined maximum rate of change is a function of the output of the electricity source.
14. The method of claim 1 , wherein the predetermined maximum rate of change is a function of the state of charge of the energy storage medium.
15. The method of claim 1 further comprising:
in response to determining that neither of conditions (a) or (b) is met:
determining whether a state of charge (SoC) of the energy storage medium is within predetermined thresholds; and
in response to determining that the SoC of the energy storage medium is outside said predetermined thresholds, transferring energy between the energy storage medium and the electricity grid to bring the SoC within said predetermined limits.
16. The method of claim 15 , wherein transferring energy between the energy storage medium and the electricity grid to bring the SOC within said predetermined thresholds comprises:
defining an upper value and a lower value for transferring energy between the energy storage medium and the electricity grid, each of which is based upon a most recent amount of electricity being supplied to the electricity grid and the maximum value for the rate of change;
determining whether the output power of the electricity source is greater than the upper value, and;
in response to determining that the output power of the electricity source is greater than the upper value, transferring energy from the electricity grid to the energy storage medium by charging the energy storage medium.
17. The method of claim 16 , further comprising:
in response to determining that the output power of the electricity source is not greater than the upper value, determining whether the output power of the electricity source is less than the lower value;
in response to determining that the output power of the electricity source is less than the lower value, transferring energy to the electricity grid from the energy storage medium; and
constraining the amount of energy transferred from the energy storage medium to the electricity grid in accordance with the lesser of the state of charge of the energy storage medium and the maximum power rating of the energy storage medium.
18. The method of claim 16 , further comprising constraining the amount of energy transferred to the energy storage medium from the electricity grid in accordance with the lesser of the unused capacity of the energy storage medium and the maximum power rating of the energy storage medium.
19. The method of claim 15 , wherein the predetermined thresholds are a function of a temporal factor.
20. A system for regulating an output power of a source of electricity that is supplied to an electricity distribution grid, comprising:
at least one energy storage medium;
a converter system that, in response to receiving a command to add energy to or absorb energy from the grid, is configured to selectively couple said at least one storage medium to the grid to transfer energy between the at least one storage medium and the grid; and
a power regulating system configured to:
determine whether:
(a) the output power of the electricity source is outside a predetermined range, and
(b) the rate of change of the output power exceeds a predefined maximum value that is a function of one or more parameters that influence an expected output of the electricity source, wherein the one or more parameters is selected from the list consisting of:
a charging constraint on charging the energy storage medium, wherein the charging constraint limits charging of the energy storage medium based on unused energy storage capacity of the energy storage medium and a maximum power rating of the energy storage medium, and
a discharging constraint on discharging the energy storage medium, wherein the discharging constraint limits discharging of the energy storage medium based on available energy storage capacity of the energy storage medium and the maximum power rating of the energy storage medium; and
control said converter system by transferring energy between the energy storage medium and the electricity grid in response to determining that either or both of conditions (a) and (b) is met,
wherein the transferring comprises discharging or charging the energy storage medium.
21. The system of claim 20 , wherein said power regulating system further includes a frequency regulating system configured to:
determine whether the operating frequency of the electricity grid is within a predetermined range of a nominal operating frequency; and
control said converter system to transfer energy between the at least one energy storage medium and the electricity grid to bring the operating frequency within said range.
22. The system of claim 21 , wherein the transferring a function of the operating frequency of the electricity grid.