Method for the computer-aided control of the power in an electrical grid

• US 9,948,103 B2
• Filed: 11/08/2013
• Issued: 04/17/2018
• Est. Priority Date: 11/15/2012
• Status: Active Grant

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Heyde, Chris Oliver, Mnz, Ulrich, Sollacher, Rudolf
• Primary Examiner(s): Suryawanshi, Suresh
• Application Number:
  US14/442,421
• Publication Number:
  US 20160276835A1
• Time in Patent Office: 1,621 Days
• Field of Search: 700295
• CPC Class Codes: G05B 13/041 in which a variable is automatically adjusted to optimise the performance
• CPC Class Codes: G06F 17/11 for solving equations , e.g. nonlinear equations, general mathematical optimization problems optimization specially adapted for a specific administrative, business or logistic context G06Q10/04
• CPC Class Codes: H02J 3/241 The oscillation concerning frequency

Abstract

A method for computer-aided control of power in an electrical grid is provided. The electrical grid has a redetermined rated frequency and includes network nodes that are interconnected via power supply lines, each of the nodes supplying power to or drawing power from the electrical grid. At least part of the nodes are provided with proportional controllers, for which a reference power and/or a proportionality factor is set, and which control the power that is supplied or drawn by each network node based on the difference between the frequency of the voltage in each network node and the rated frequency of the electrical grid. The reference power and the proportionality factor of at least some of the proportional controllers are determined on the basis of solving an optimization problem. The stability and robustness of the operation of the electrical grid is optimized without the need for carrying out complex simulations.

Claims

1. A method for computer-aided control of power in an electrical grid, wherein the electrical grid has a preset rated frequency and comprises a plurality of nodes, which are connected to one another via electrical lines and each feed power into the electrical grid or draw power from the electrical grid, wherein the power fed into or drawn from the respective nodes is given via a proportionality relationship, in accordance with which, in a preset frequency range of the voltages at the respective node, the power is set on the basis of a reference power, which is the drawn or fed power at the preset rated frequency, and on the basis of a proportionality factor depending on a difference between a frequency of the voltage in the respective node and the preset rated frequency of the electrical grid, wherein a proportional controller is provided in at least some of the nodes, for which the proportional controller, the reference power, and/or the proportionality factor is set, wherein:

a) a steady state of the electrical grid is modeled in which a constant frequency is set for all of the voltages of the nodes;

b) an optimization problem is solved and hereby reference powers and proportionality factors are determined for at least some of the proportional controllers, wherein the optimization problem is defined on a basis of a condition for the modeled steady state, wherein when the condition is met, the phase differences between the voltages of adjacent nodes are each less than or less than or equal to a maximum phase value; and

c) the at least some of the proportional controllers are set to the reference powers and proportionality factors determined in step b);

further wherein the optimization problem is converted into a convex optimization problem.

2. The method as claimed in claim 1, wherein the proportionality relationship in the respective nodes is as follows:

{tilde over (p)}_i={tilde over (p)}_i0−

k<sub>θ

i</sub>(_i−

ω

₀),

wherein {tilde over (p)}_i is the power fed or drawn by a respective node i;

wherein {tilde over (p)}_i0 is the sum of the reference power p_i0 and the local load p_u in the node i;

wherein k<sub>θ

i</sub> is the proportionality factor in the node i;

wherein _i is the frequency of the voltage of the node i;

wherein ω

₀ is the rated frequency of the electrical grid.

3. The method as claimed in claim 1, wherein the steady state of the electrical grid is modeled on the basis of a dynamic physical model, wherein the dynamic physical model describes the time profile of the phases of the voltages in the respective nodes as a function of parameters of the electrical grid comprising the reference powers and proportionality factors of the proportionality relationships.

4. The method as claimed in claim 3, wherein the dynamic physical model comprises a system of coupled differential equations, wherein a respective differential equation represents the time profile of the phase of the voltage of a node.

5. The method as claimed in claim 4, wherein the system of coupled differential equations represents a physical oscillation equation system.

6. The method as claimed in claim 5, wherein the oscillation equation system is as follows:

M_ii+k<sub>θ

ii</sub>=k<sub>θ

i</sub>ω

₀+{tilde over (p)}_i0−

p_iL−

Σ

<sub>jϵ

Ni</sub>b_iju_iu_j sin({tilde over (θ

)}_i−

{tilde over (θ

)}_j),

where M_i is the moment of inertia of a mass coupled to the electrical grid in the respective node i;

where _i is the derivative of the frequency of the voltage in the respective node i;

where {tilde over (θ

)}_i and {tilde over (θ

)}_j are the phase of the voltage in the respective node i and j, respectively;

where N_i represents the amount of nodes adjacent to a respective node i;

where u_i and u_j are the rms values of the voltages in the respective nodes i and j, respectively;

where b_ij is the susceptance of the electrical line between nodes i and j.

7. The method as claimed in claim 1, wherein the steady state of the electrical grid is modeled on a basis of load flow equations for the real powers generated in the respective nodes.

8. The method as claimed in claim 7, wherein the condition whereby the ohmic resistance on the electrical lines between adjacent nodes in the electrical grid is negligibly low in comparison with the reactance on the electrical lines between adjacent nodes is taken into consideration in the load flow equations.

9. The method as claimed in claim 7, wherein the load flow equation for a respective node i is as follows:

10. The method as claimed in claim 1, wherein the condition for the modeled steady state is as follows:

11. The method as claimed in claim 1, wherein, during the solution of the optimization problem, it is considered, as boundary condition, that the reference powers of at least some of the proportional controllers are within a predetermined interval.

12. The method as claimed in claim 1, wherein, during the solution of the optimization problem, it is considered, as boundary condition, that the reference powers of the proportionality relationships of all of the nodes fluctuate within a predetermined fluctuation degree.

13. The method as claimed in claim 12, wherein the fluctuation degree is defined in such a way that the fluctuation in the reference power of the proportionality relationship of each node is less than or less than or equal to a predetermined value.

14. The method as claimed in claim 1, wherein the fluctuation degree is defined in such a way that a sum and in particular a weighted sum of the fluctuations in the reference powers of the proportionality relationships of all of the nodes is less than or less than or equal to a predetermined value.

15. The method as claimed in claim 1, wherein, during the solution of the optimization problem, it is considered, as boundary condition, that the line frequency set in the steady state in the electrical grid deviates from the rated frequency of the electrical grid by less than a predetermined frequency value.

16. The method as claimed in claim 15, wherein at least some of the nodes have available primary control power for the electrical grid, wherein, from the boundary condition whereby the line frequency set in the steady state in the electrical grid deviates from the rated frequency by less than a predetermined frequency value, a further boundary condition is derived which is taken into consideration in the solution of the optimization problem and in accordance with which the respective primary control powers are less than or less than or equal to a predetermined threshold value.

17. The method as claimed in claim 15, wherein step b) is implemented a number of times for ever decreasing predetermined frequency values until the minimized maximum value resulting in step b) from the solution of the optimization problem exceeds a predetermined threshold, wherein the at least some of the proportional controllers is set to the reference powers and proportionality factors which result from step b) directly prior to the predetermined threshold being exceeded.

18. The method as claimed in claim 1, wherein the optimization problem describes the minimization of a cost function, which is greater than the maximum phase value.

19. The method as claimed in claim 18, wherein the cost function comprises, as single team, the maximum phase value, or in that the cost function comprises a sum of a term of the maximum phase value and one or more further terms, wherein the further term(s) is/are preferably configured in such a way that at least one of the further terms is greater than the power fed by the nodes and/or the lower the power drawn by the nodes and/or the greater the primary control power that the nodes have available.

20. The method as claimed in claim 1, wherein the optimization problem describes the minimization of a cost function which is independent of the maximum phase value, wherein, as boundary condition of the optimization problem, it is considered that the maximum phase value is less than a preset threshold value.

21. An apparatus for computer-aided control of power in an electrical grid, wherein the electrical grid has a preset rated frequency and comprises a plurality of nodes, which are connected to one another via electrical lines and which each feed power into the electrical grid or draw power from the electrical grid, wherein the power fed in or drawn by the respective nodes is given via a proportionality relationship, in accordance with which, in a preset frequency range of the voltages in the respective node, the power is set on the basis of a reference power, which is the drawn or fed power at rated frequency, and a proportionality factor depending on a difference between the frequency of the voltage in the respective node and the preset rated frequency of the electrical grid, wherein a proportional controller is provided in at least some of the nodes, for which the proportional controller the reference power and/or the proportionality factor is set, wherein the apparatus is designed for implementing a method in which:

a) a steady state of the electrical grid is modeled in which a constant frequency is set for all of the voltages of the nodes;

b) an optimization problem is solved and hereby reference powers and proportionality factors are determined for at least some of the proportional controllers, wherein the optimization problem is defined on the basis of a condition for the modeled steady state, wherein when said condition is met, the phase differences between the voltages of adjacent nodes are each less than or less than or equal to a maximum phase value;

c) the at least some of the proportional controllers are set to the reference powers and proportionality factors determined in step b);

wherein the optimization problem is converted into a convex optimization problem.

22. An electrical grid, which has a preset rated frequency and comprises a plurality of nodes, which are connected to one another via electrical lines and which each feed power into the electrical grid or draw power from the electrical grid during operation, wherein the power fed or drawn by the respective nodes is given via a proportionality relationship, in accordance with which, in a preset frequency range of the voltages in the respective node, the power is set on the basis of a reference power, which is the drawn or fed power at the rated frequency, and a proportionality factor (k1, in dependence on a difference between the frequency of the voltage in the respective node and the preset rated frequency of the electrical grid, wherein a proportional controller is provided in at least some of the nodes, for which the proportional controller the reference power and/or the proportionality factor is set, wherein the electrical grid comprises an apparatus for computer-aided control of the generated power as claimed in claim 21.