Power ramp rate control for renewable variable power generation systems
Certain embodiments of the invention may include systems and methods for controlling power ramp rates in renewable variable power generation systems. According to an exemplary embodiment of the invention, a method is provided for limiting power ramp rates. The method can include regulating collective power output of a plurality of variable energy sources by monitoring collective power output of the plurality of variable energy sources, and controlling collective power output of the plurality of variable energy sources with the plurality of power control signals.
1. A method for regulating collective power output of a plurality of variable energy sources, the method comprising:
monitoring collective power output of the plurality of variable energy sources;
predicting future collective available power levels of the plurality of variable energy sources based at least in part on a first desired collective power ramp rate over a first time duration and a second desired collective power ramp rate over a second time duration, wherein the predicting of the future collective available power levels comprises:
establishing an average ramp rate for each time duration calculated as (X n −X n−N+1 ), wherein X n is a power output at n th time period and N is the total number of time periods in the time duration;
determining the future collective available power levels based on the average ramp rate; and
comparing the future collective available power levels to a settable ramp rate limit;
based on the comparison, modifying, using at least one modifying function, the predicted collective available power levels based at least in part on limiting the rate of change of the predicted collective available power levels depending upon a direction of power change, wherein the at least one modifying function provides for faster slew rates when reducing power, to rapidly correct a transient condition, and slower slew rates when increasing power, wherein the at least one modifying function includes a low pass filter and a slew rate limiter;
determining a power regulation setpoint based on the modified predicted collective available power levels;
selecting a minimum of the collective available power levels and the power regulation setpoint;
based at least in part on the selection, generating a net power command signal based at least in part on the modified predicted collective available power levels;
generating a plurality of power control signals based at least in part on the net power command signal; and
controlling collective power output of the plurality of variable energy sources with the plurality of power control signals to allow different collective rates of change of power output depending upon the direction of power change or upon previous power changes, wherein the collective rate of change of power output of the variable energy sources does not exceed a first desired collective power ramp rate over the first time duration.
2. The method of claim 1 , wherein the predicted collective available power levels are operable to control collective power output of the variable energy sources wherein the collective rate of change of power output of the variable energy sources does not exceed the first desired collective power ramp rate over the first the duration and does not exceed the second desired collective power ramp rate over the second time duration.
3. The method of claim 2 , wherein modifying the predicted collective available power levels is based at least in part on a desired collective power ramp rate.
4. The method of claim 1 , wherein controlling collective power output of the plurality of variable energy sources further comprises communicating a power reference signal to the plurality of variable energy sources wherein the power reference signal is determined as a minimum of the modified predicted collective available power levels and the power regulator setpoint.
5. The method of claim 1 , wherein controlling collective power output of the plurality of variable energy sources is further based on power ratings of the plurality of variable energy sources.
6. The method of claim 1 , wherein determining a power regulation setpoint comprises providing an active power setpoint or an apparent power setpoint.
7. A variable energy power regulator system, comprising a controller operable to:
monitor collective power output of a plurality of variable energy sources;
predict future collective available power levels of the plurality of variable energy sources based at least in part on a first desired collective power ramp rate over a first time duration and a second desired collective power ramp rate over a second time duration, wherein the predicting of the future collective available power levels comprises:
establishing an average ramp rate for each time duration calculated as (X n −X n−N+1 ), wherein X n is a power output at n th time period and N is the total number of time periods in the time duration;
determining the future collective available power levels based on the average ramp rate; and
comparing the future collective available power levels to a settable ramp rate limit;
based on the comparison, modify, using at least one modifying function, the predicted collective available power levels based at least in part on limiting the rate of change of the predicted collective available power levels depending upon a direction of power change to produce a modified predicted collective available power levels, wherein the at least one modifying function provides for faster slew rates when reducing power, to rapidly correct a transient condition, and slower slew rates when increasing power, wherein the at least one modifying function includes a low pass filter and a slew rate limiter;
determine a power regulation setpoint based on the modified predicted collective available power levels;
select a minimum of the collective available power levels and the power regulation setpoint;
based at least in part on the selection, generate a net power command signal based at least in part on the modified predicted collective available power levels;
generate a plurality of power control signals based at least in part on the net power command signal; and
control collective power output of the plurality of variable energy sources with the plurality of power control signals to allow different collective rates of change of power output depending upon the direction of power change or upon previous power changes, wherein the collective rate of change of power output of the variable energy sources does not exceed a first desired collective power ramp rate over the first time duration.
8. The system of claim 7 , wherein the predicted collective available power levels are operable to control collective power output of the variable energy sources wherein the collective rate of change of power output of the variable energy sources does not exceed the first desired collective power ramp rate over the first time duration and does not exceed the second desired collective power ramp rate over the second time duration.
9. The system of claim 7 , wherein the controller is further operable to modify the predicted collective available power levels based at least in part on a desired collective power ramp rate.
10. The system of claim 7 , wherein the controller is further operable to control collective power output of the plurality of variable energy sources by communicating a power reference signal to the plurality of variable energy sources, wherein the power reference signal is determined as the minimum of the modified predicted collective available power levels and the power regulator setpoint.
11. The system of claim 7 , wherein the controller is further operable to control collective power output of the plurality of variable energy sources based on power ratings of the plurality of variable energy sources.
12. The system of claim 7 , wherein the controller is further operable to generate a power regulation setpoint comprising an active power setpoint or an apparent power setpoint.
13. A solar farm, comprising:
a plurality of variable energy sources and inverters operable to collectively supply electrical power to a utility system; and
a variable energy power regulator system operable to:
monitor collective power output of the plurality of variable energy sources and inverters;
predict future collective available power levels of the plurality of variable energy sources and inverters based at least in part on a first collective power ramp rate limit over a first ramp rate time duration and a second predicted available power based on a second collective power ramp rate limit over a second time duration, wherein the predicting of the future collective available power levels comprises:
establishing an average ramp rate for each time duration calculated as (X n −X n−N+1 ), wherein X n is a power output at n th time period and N is the total number of time periods in the time duration;
determining the future collective available power levels based on the average ramp rate; and
comparing the future collective available power levels to a settable ramp rate limit;
based on the comparison, modify, using at least one modifying function, the predicted collective available power levels based at least in part on limiting the rate of change of the predicted collective available power levels depending upon a direction of power change, wherein the at least one modifying function provides for faster slew rates when reducing power, to rapidly correct a transient condition, and slower slew rates when increasing power, wherein the at least one modifying function includes a low pass filter and a slew rate limiter;
determine a power regulation setpoint based on the modified predicted collective available power levels;
select a minimum of the collective available power levels and the power regulation setpoint;
based at least in part on the selection, generate a net farm power command signal based at least in part on the modified predicted collective available power levels;
generate a plurality of power control signals based at least in part on the net farm power command signal; and
control collective power output of the plurality of variable energy sources and inverters with the plurality of power control signals to allow different collective rates of change of power output depending upon the direction of power change or upon previous power changes, wherein the collective rate of change of power output of the variable energy sources does not exceed a first desired collective power ramp rate over the first time duration.
14. The solar farm of claim 13 , wherein the processor is further operable to control collective power output of the plurality of variable energy sources by communicating a power reference signal to the plurality of variable energy sources and inverters via a closed loop PID feedback control system, wherein the power reference signal is determined as the minimum of the modified predicted collective available power levels and the power regulator setpoint.
15. The solar farm of claim 13 , wherein the processor is further operable to modify the predicted collective available power levels based at least in part on desired collective power ramp rates.
16. The solar farm of claim 13 , wherein the processor is further operable to control collective power output of the plurality of variable energy sources and inverters based on power ratings of the plurality of variable energy sources and inverters.
17. The solar farm of claim 13 , wherein the processor is further operable to generate a power regulation setpoint comprising an active power setpoint or an apparent power setpoint.