Load controller and method to enhance effective capacity of a photovoltaic power supply using a dynamically determined expected peak loading

• US 20030182023A1
• Filed: 03/18/2003
• Published: 09/25/2003
• Est. Priority Date: 05/21/1998
• Status: Active Grant

• Current Assignee: The Research Foundation for The State University of New York (State University of New York)
• Original Assignee: The Research Foundation for The State University of New York (State University of New York)
• Inventors: Perez, Richard
• Granted Patent: US 6,889,122 B2
• Time in Patent Office: Days
• US Class Current: 700/295
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 2300/28 The renewable source being wind energy wind motors F03D
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

A load controller and method are provided for maximizing effective capacity of a non-controllable, renewable power supply coupled to a variable electrical load also coupled to a conventional power grid. Effective capacity is enhanced by monitoring power output of the renewable supply and loading, and comparing the loading against the power output and a load adjustment threshold determined from an expected peak loading. A value for a load adjustment parameter is calculated by subtracting the renewable supply output and the load adjustment parameter from the current load. This value is then employed to control the variable load in an amount proportional to the value of the load control parameter when the parameter is within a predefined range. By so controlling the load, the effective capacity of the non-controllable, renewable power supply is increased without any attempt at operational feedback control of the renewable supply.

Claims

1. A method for increasing effective capacity of a photovoltaic power supply coupled to a power grid and a variable load, said variable load being powered by said power grid and said photovoltaic power supply, said method comprising:

(a) determining photovoltaic power supply output and current loading of said variable load, the current loading being a current value of the variable load in the absence of the photovoltaic power supply;

(b) determining an expected peak loading of said variable load for a defined time interval and ascertaining therefrom a load adjustment threshold;

(c) determining a value for a load adjustment parameter from said photovoltaic power supply output, said current loading and said load adjustment threshold, said load adjustment parameter being defined as said current loading less said photovoltaic power supply output less said load adjustment threshold; and

(d) controlling said variable load employing said value of said load adjustment parameter to increase the effective capacity of said photovoltaic power supply without operational feedback control of said photovoltaic power supply.

2. The method of claim 1, wherein said determining (a) further comprises determining the current loading of the variable load in the absence of the photovoltaic power supply and in the absence of the controlling (d) of the variable load.

3. The method of claim 1, wherein said determining (b) comprises setting an initial expected peak loading at a start of the defined time interval and reevaluating the expected peak loading within the defined time interval with reference to variations in the variable load, said reevaluating comprising increasing the expected peak loading when the variable load exceeds the expected peak loading, and wherein said reevaluating and increasing comprise:

4. The method of claim 3, wherein the measured value of the variable load (LD), the measured photovoltaic power supply output (PV), and the estimated load change due to said controlling (d) (SLCLD) are determined as rolling averages within a defined measurement time interval.

5. The method of claim 1, wherein:

said controlling (d) comprises adjusting current loading of the variable load if the value of the load adjustment parameter exceeds zero, wherein said adjusting is proportional to said value;

said controlling (d) further comprises adjusting an operating threshold of at least one load component of the variable load;

said method further comprises predefining a maximum possible action and wherein said adjusting of said operational threshold comprises adjusting said operational threshold proportional to said value up to said maximum possible action; and

wherein said variable load comprises a temperature load, and said maximum possible action comprises a maximum acceptable level of temperature change.

6. The method of claim 5, wherein said determining (a) further comprises determining the current loading of the variable load in the absence of the photovoltaic power supply and in the absence of the controlling (d) of the variable load, said controlling (d) of the variable load resulting in an estimated load change determined as:

7. The method of claim 6, further comprising defining two parameters SLCLD_long and SLCLD_short, wherein SLCLD_long is a running mean average of PA·

KWD over N minutes, where N is a user estimated amount of time necessary for a temperature adjustment to have full impact on the variable load, and SLCLD_short is a running mean average of PA·

KWD over M minutes, where M is a user defined time interval, and M<

N; and

wherein;

LOAD=LD+PV+Min(SLCLD_short, SLCLD_long) LOAD′

=LD+PV+Max(SLCLD_short, SLCLD_long)

where

LOAD=a parameter used to update a value for the expected peak loading determined by said determining (b);

LOAD′

=a parameter used to calculate the parameter PA (i.e., a current amount of operational threshold adjustment by said adjusting);

LD=measured value of the variable load

PV=measured photovoltaic power supply output

SLCLD_short=running mean average of PA·

KWD over N minutes;

SLCLD_long=running mean average of PA·

KWD over M minutes, where M<

N.

8. The method of claim 1, wherein:

said controlling (d) comprises adjusting current loading of the variable load if the value of the load adjustment parameter exceeds zero, wherein the adjusting is proportional to said value;

said controlling (d) further comprises adjusting an operating threshold of at least one load component of the variable load;

said method further comprises predefining a maximum possible action and wherein said adjusting of said operational threshold comprises adjusting said operational threshold proportional to said value up to said maximum possible action;

wherein said variable load comprises a temperature load, and said maximum possible action comprises a maximum acceptable level of temperature change; and

wherein;

PA=Max(PA_now, PA_old−

MPA/q)

where;

PA=a temperature adjustment request;

PA_now=is a current temperature adjustment request

PA_old=is a previous temperature adjustment request

MPA=predefined maximum possible action

q=a user selected parameter.

9. The method of claim 1, wherein the variable load comprises a variable cooling temperature load, said controlling (d) further comprises adjusting an operating threshold of at least one load component of the variable load, and wherein when said adjusting results in an increase in cooling temperature, said increase in cooling temperature being accomplished without use of any heating system associated with the variable load.

10. A load controller for controlling a variable load coupled to a power grid and a photovoltaic power supply, said load controller comprising:

(i) means for determining photovoltaic power supply output and current loading of the variable load, said means for determining (i) comprising means for ascertaining a current value of the variable load in the absence of the photovoltaic power supply;

(ii) means for determining an expected peak loading of said variable load for a defined time interval and for ascertaining therefrom a load adjustment threshold;

(iii) means for determining a value for a load adjustment parameter based on said photovoltaic power supply output, said current loading, and said load adjustment threshold, said load adjustment parameter being defined as said current loading less said photovoltaic power supply output less said load adjustment threshold; and

(iv) means for controlling said variable load employing said value of said load adjustment parameter to increase the effective capacity of said photovoltaic power supply.

11. The load controller of claim 10, wherein said means for determining (i) further comprises means for determining the current loading of the variable load in the absence of the photovoltaic power supply and in the absence of the means for controlling (iv) the variable load.

12. The load controller of claim 10, wherein said means for determining (ii) comprises means for setting an initial expected peak loading at a start of the predefined time interval and for reevaluating the expected peak loading within the defined time interval with reference to variations in the variable load, said means for reevaluating comprising means for increasing the expected peak loading when the variable load exceeds the expected peak loading, and wherein said means for reevaluating and means for increasing comprise:

13. The load controller of claim 12, wherein the measured value of the variable load (LD), the measured photovoltaic power supply output (PV), and the estimated load change due to said means for controlling (iv) (SLCLD) are determined as rolling averages within a predefined measurement time interval.

14. The load controller of claim 10, wherein:

said means for controlling (iv) comprises means for adjusting current loading of the variable load if the value of the load adjustment parameter exceeds zero, wherein said adjusting is proportional to said value;

said means for controlling (iv) further comprises means for adjusting an operating threshold of at least one load component of the variable load;

said load controller comprises means for predefining a maximum possible action and wherein said means for adjusting said operational threshold comprises means for adjusting said operational threshold proportional to said value up to said maximum possible action; and

wherein said variable load comprises a temperature load, and said maximum possible action comprises a maximum acceptable level of temperature change.

15. The load controller of claim 14, wherein said means for determining (i) further comprises means for determining the current loading of the variable load in the absence of the photovoltaic power supply and in the absence of said means for controlling (iv) the variable load, said means for controlling (d) the variable load resulting in an estimated load change determined as:

16. The load controller of claim 15, wherein two parameters SLCLD_long and SLCLD_short are defined, SLCLD_long being a running mean average of PA·

KWD over N minutes, where N is a user estimated amount of time necessary for a temperature adjustment to have full impact on the variable load, and SLCLD_short being a running mean average of PA·

KWD over M minutes, where M is a user defined time interval, and M<

N; and

wherein;

LOAD=LD+PV+Min(SLCLD_short, SLCLD_long) LOAD′

=LD+PV+Max(SLCLD_short, SLCLD_long)

where

LOAD=a parameter used to update a value for the expected peak loading determined by said means for determining (ii);

LOAD′

=a parameter used to calculate the parameter PA (i.e., a current amount of operational threshold adjustment by said adjusting);

LD=measured value of the variable load

PV=measured photovoltaic power supply output

SLCLD_short=running mean average of PA·

KWD over N minutes;

SLCLD_long=running mean average of PA·

KWD over M minutes, where M<

N.

17. The load controller of claim 10, wherein:

said means for controlling (iv) comprises means for adjusting current loading of the variable load if the value of the load adjustment parameter exceeds zero, wherein the adjusting is proportional to said value;

said means for controlling (iv) further comprises means for adjusting an operating threshold of at least one load component of the variable load;

said load controller further comprises means for predefining a maximum possible action and wherein said means for adjusting of said operational threshold comprises means for adjusting said operational threshold proportional to said value up to said maximum possible action;

wherein said variable load comprises a temperature load, and said maximum possible action comprises a maximum acceptable level of temperature change; and

wherein;

PA=Max(PA_now, PA_old−

MPA/q)

where;

PA=a temperature adjustment request;

PA_now=is a current temperature adjustment request

PA_old=is a previous temperature adjustment request

MPA=predefined maximum possible action

q=a user selected parameter.

18. The load controller of claim 10, wherein the variable load comprises a variable cooling temperature load, said means for controlling (iv) further comprises means for adjusting an operating threshold of at least one load component of the variable load, and wherein when said means for adjusting results in an increase in cooling temperature, said increase in cooling temperature being accomplished without use of any heating system associated with the variable load.