Method and apparatus for direct control of the inter-area dynamics in large electric power systems

• US 5,517,422 A
• Filed: 10/12/1993
• Issued: 05/14/1996
• Est. Priority Date: 10/12/1993
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Liu, Xiaojun, Ilic, Marija
• Primary Examiner(s): Cosimano, Edward R.
• Assistant Examiner(s): KEMPER, MELANIE A
• Application Number:
  US08/134,280
• Time in Patent Office: 945 Days
• Field of Search: 364/492, 364/493, 364/483, 361/139, 307/57, 307/52, 307/153
• US Class Current: 700/286
• CPC Class Codes: H02J 3/004 Generation forecast, e.g. methods or systems for forecasting future energy generation
• CPC Class Codes: H02J 3/06 Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
• CPC Class Codes: Y02B 70/3225 Demand response systems, e.g. load shedding, peak shaving
• CPC Class Codes: Y04S 10/50 Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
• CPC Class Codes: Y04S 20/222 Demand response systems, e.g. load shedding, peak shaving

Abstract

A method and apparatus for directly controlling the net power flow on tie lines between different areas of a large electric power system, which provides automatic dynamic control to maintain the stability of the system. Utilizing a sensitivity matrix and simple measurements of real power output from each of the generators in a given area, it is possible to dynamically control the entire system in a way which accounts for loading changes in any area. The control can be implemented using a Flexible AC Transmission Systems (FACTS) technology controller which utilizes the measurements and sensitivity matrix from a given area to determine a derived net power flow from the first area to the remainder of the system, and for comparing the derived net power flow to a set point to provide an error signal which approaches zero as the controller adjusts, for example, a phase angle difference across the tie line to adjust the net power flow thereon. Alternatively, the derived net power flow can be used for scheduling the generation of power in a given area and/or to control a local controller at the generator level.

Claims

1. In an electrical power system which includes a plurality of areas with generators and loads, the areas being electrically connected by tie lines, the improvement comprising:

means for measuring a real power output of each generator in a first area, and generating a measurement signal indicative thereof;

means, responsive to the measurement signal, for deriving a net power flow from the first area to the remainder of the system along the tie lines, and generating a derivation signal indicative thereof; and

means, responsive to the derivation signal, connected to at least one tie line from the first area for directly and dynamically controlling the actual net power flow from the first area to the remainder of the system along the tie lines,

wherein the deriving means determines a weighted sum of the real power outputs from the generators in the first area which are weighted with respect to the electrical distance of each generator from a location on the tie line where the control is applied.

2. The system of claim 1, wherein the means for controlling are connected to each of the tie lines to cause the actual net power flow to approach a desired value.

3. The system of claim 1, wherein the control means compares the derivation signal to a desired net power flow and determines a net error signal.

4. The system of claim 3, wherein the control means directly adjusts the actual power flow on at least one tie line in order to cause the net error signal to approach zero.

5. The system of claim 1, wherein the control means includes means for adjusting a voltage phase angle difference across the tie line where the control is applied.

6. The system of claim 1, wherein the control means includes means for adjusting the magnitude and phase angle of a voltage at one end of the tie line where the control is applied.

7. The system of claim 1, wherein the control means comprises a static phase shifter transformer having an electronically controlled tap position.

8. The system of claim 1, wherein the control means incorporates Flexible AC Transmission Systems (FACTS) technology.

9. The system of claim 1, wherein the control means comprises means for converting an alternating current signal at one end of the tie line to a direct current signal, and means at the other end of the tie line for converting the direct current signal to an alternating current signal.

10. The system of claim 9, wherein the control means comprises an HVDC transmission line.

11. The system of claim 1, wherein the control means provides stabilization of the inter-area dynamics in the frequency range of below about 1 Hz.

12. The system of claim 1, wherein the control means suppresses inter-area oscillations.

13. The system of claim 1, wherein the measuring means converts an analog real power output from the first area to a digital measurement signal and the deriving means is a digital processor which processes the digital measurement signal.

14. The system of claim 1, wherein the derived net power flow yⁱ is determined from:

space="preserve" listing-type="equation">y.sup.i =p.sup.i P.sub.G.sup.i (a)

where

pⁱ is a participation factor;

p_Gⁱ is a set of the real power outputs from each of the generators in the first area; and

i designates the first area having a plurality of generators G and loads L electrically connected by a network N;

and wherein pⁱ is calculated from;

space="preserve" listing-type="equation">p.sup.i K.sub.p.sup.i =0 (b)

where;

K_pⁱ is an effective participation factor of generator and load power in derived net power flow yⁱ, and is defined by;

space="preserve" listing-type="equation">K.sub.p.sup.i =J.sub.GG +J.sub.GL C.sub.ω

(c)

where;

C.sub.ω

represents for a contribution of power changes at loads in derived net power flow yⁱ, and is defined by;

space="preserve" listing-type="equation">C.sub.ω

=-J.sub.LL J.sub.LG (d)

where J is a sensitivity matrix of real power flows into the network with respect to phase angles, and is defined by;

##EQU16## where P^N is a complex power flow defined by;

space="preserve" listing-type="equation">P.sup.N =(P.sub.G.sup.N, P.sub.L.sup.N) (f)

where

P_G^N is a set of all real power flows from all generators in area i into the network

P_L^N is a set of all real power flows from all loads in area i into the network N;

and where i is a complex phase angle defined by;

space="preserve" listing-type="equation">δ

=(δ

.sub.G, δ

.sub.L) (g)

where;

δ

_G is a set of all voltage phase angles of all generators in area i;

δ

_L is a set of all voltage phase angles of all loads in area i;

and where;

J_GG is a sensitivity submatrix (∂

P_G^N /∂

δ

_G) of net power flows out of generators with respect to generator phase angle;

J_LG is a sensitivity submatrix (∂

P_L^N /∂

δ

_G) of net power flows out of loads with respect to generator phase angle;

J_GL is a sensitivity submatrix (∂

P_G^N /∂

δ

_L) of net power flows out of generators with respect to load phase angle;

J_LL is a sensitivity submatrix (∂

P_L^N /∂

δ

_L) of net power flows out of loads with respect to load phase angle;

where all voltages are measured between a node in the network and ground.

15. The system of claim 1, comprising a plurality of areas connected by a plurality of tie lines, and the control means comprising a plurality of controllers positioned on different tie lines which control the actual net power flow from different areas.

16. In a method for controlling the net power flow in an electrical power system which includes a plurality of areas with generators and loads, the areas being electrically connected by tie lines, the improvement comprising:

measuring a real power output of each generator in a first area, and generating a measurement signal indicative thereof;

deriving, in response to the measurement signal, a net power flow from the first area to the remainder of the system along the tie lines, and generating a derivation signal indicative thereof; and

dynamically controlling, in response to the derivation signal, the actual net power flow from the first area to the remainder of the system along the tie lines by directly and dynamically controlling the actual net power flow on at least one tie line from the first area, and determining locations in the system at which the dynamic control is applied.

17. The method of claim 16, wherein the controlling step includes controlling the actual net power flow on each tie line to cause the actual net power flow to approach a desired value.

18. The method of claim 16, wherein the deriving step includes determining a weighted sum of real power outputs from the generators in the first area which are weighted with respect to the electrical distance of each generator from a location on the tie line where the control is applied.

19. The method of claim 18, wherein the derived net power flow yⁱ is determined from:

space="preserve" listing-type="equation">y.sup.i =p.sup.i P.sub.G.sup.i (a)

where

pⁱ is a participation factor;

P_Gⁱ is a set of the real power outputs from each of the generators in the first area; and

i designates the first area having a plurality of generators G and loads L electrically connected by a network N;

and wherein pⁱ is calculated from;

space="preserve" listing-type="equation">p.sup.i K.sub.p.sup.i =0 (b)

where;

K_pⁱ is an effective participation factor of generator and load power in derived net power flow yⁱ, and is defined by;

space="preserve" listing-type="equation">K.sub.p.sup.i =J.sub.GG +J.sub.GL C.sub.ω

(c)

where;

C.sub.ω

represents for a contribution of power changes at loads in derived net power flow yⁱ, and is defined by;

space="preserve" listing-type="equation">C.sub.ω

=-J.sub.LL J.sub.LG (d)

where J is a sensitivity matrix of real power flows into the network with respect to phase angles, and is defined by;

##EQU17## where P^N is a complex power flow defined by;

space="preserve" listing-type="equation">P.sup.N =(P.sub.G.sup.N, P.sub.L.sup.N) (f)

where

P_G^N is a set of all real power flows from all generators in area i into the network N;

P_L^N is a set of all real power flows from all loads in area i into the network N;

and where δ

is a complex phase angle defined by;

space="preserve" listing-type="equation">δ

=(δ

.sub.G, δ

.sub.L) (g)

where;

δ

_G is a set of all voltage phase angles of all generators in area i;

δ

_L is a set of all voltage phase angles of all loads in area i;

and where;

J_GG is a sensitivity submatrix (∂

P_G^N /∂

δ

_G) of net power flows out of generators with respect to generator phase angle;

J_LG is a sensitivity submatrix (∂

P_L^N /∂

δ

_G) of net power flows out of loads with respect to generator phase angle;

J_GL is a sensitivity submatrix (∂

P_G^N /∂

δ

_L) of net power flows out of generators with respect to load phase angle;

J_LL is a sensitivity submatrix (∂

P_L^N /∂

δ

_L) of net power flows out of loads with respect to load phase angle;

where all voltages are measured between a node in the network and ground.

20. The method of claim 16, wherein the controlling step includes comparing the derivation signal to a desired net power flow and determining a net error signal.

21. The method of claim 20, wherein the controlling step includes directly adjusting the actual net power flow on at least one tie line in order to cause the net error signal to approach zero.

22. The method of claim 16, wherein the controlling step includes adjusting a voltage phase angle difference across the tie line where the control is applied.

23. The method of claim 16, wherein the controlling step includes adjusting the magnitude and phase angle of a voltage at one end of the tie line where the control is applied.

24. The method of claim 16, wherein the controlling step comprises providing a static phase shifter transformer on the tie line and electronically controlling the tap position thereof.

25. The method of claim 16, wherein the controlling step comprises applying high speed switching to alter the electrical characteristics of at least one tie line.

26. The method of claim 16, wherein the controlling step comprises converting an alternating current signal at one end of the tie line to a direct current signal, and converting at the other end of the tie line the direct current signal to an alternating current signal.

27. The method of claim 26, wherein the controlling step comprises utilizing an HVDC apparatus.

28. The method of claim 16, wherein the controlling step provides stabilization of the inter-area dynamics in the frequency range of below about 1 Hz.

29. The method of claim 16, wherein the controlling step suppresses inter-area oscillations.

30. The method of claim 16, wherein the system comprises a plurality of areas connected by a plurality of tie lines, and the controlling step is provided by a plurality of controllers positioned on different tie lines which control the actual net power flow from different areas.

31. The method of claim 16, wherein the locations are determined by the electrical distances of the loads and generators in a given area to an associated tie line.

32. In an electrical power system which includes a plurality of areas with generators and loads, the areas being electrically connected by tie lines, and the generators and loads within a given area being electrically connected by a network, the improvement comprising:

means for measuring a real power output of each generator in a first area, and generating a measurement signal indicative thereof;

a computer, which receives the measurement signal, and derives a net power flow from the first area to the remainder of the system along the tie lines and which derived net power flow accounts for transmission losses within a network of the first area and determines a weighted sum of the real power outputs from the generators in the first area which are weighted with respect to the electrical distance of each generator from a location on the tie line where control is applied, the computer generating a derivation signal indicative thereof; and

means, responsive to the derivation signal and connected to at least one tie line from the first area, for directly and dynamically controlling the actual net power flow from the first area to the remainder of the system along the tie lines.

33. The system of claim 32, wherein the computer includes means for scheduling the generation of power within the first area to meet the dynamic power transfer requirements from the first area to the other areas.

34. The system of claim 32, wherein the first area includes at least one generator with a local generator control means, and the computer generates a control signal for use by the local generator control means in controlling the real power output of the generator.

35. The system of claim 32, wherein the means for controlling are connected to each of the tie lines to cause the actual net power flow to approach a desired value.

36. In a method of controlling the net power flow in an electrical power system which includes a plurality of areas with generators and loads, the areas being electrically connected by tie lines, and the generators and loads within a given area being electrically connected by a network, the improvement comprising:

measuring a real power output of each generator in a first area, and generating a measurement signal indicative thereof;

deriving, in response to the measurement signal, a net power flow from the first area to the remainder of the system along the tie lines, and which derived net power flow accounts for transmission losses within a network of the first area and determines a weighted sum of the real power outputs from the generators in the first area which are weighted with respect to the electrical distance of each generator from a location on the tie line where the control is applied, and generating a derivation signal indicative thereof; and

dynamically controlling, in response to the derivation signal, the actual net power flow from the first area to the remainder of the system along the tie lines by directly and dynamically controlling the actual net power flow on at least one tie line from the first area.

37. The method of claim 36, further comprising utilizing the derived net power flow for scheduling the generation of power within the first area to meet the dynamic power transfer requirements from the first area to other areas.

38. The method of claim 36, wherein the first area includes at least one local generator control means and the computer generates a control signal for use by the local generator control means in controlling the real power output of the generator.

39. The method of claim 36, wherein the controlling step includes controlling the actual net power flow on each tie line to cause the actual net power flow to approach a desired value.