# US 12,009,771 B1 · Doubly fed induction generator speed control system and method for controlling the system

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- Number: US 12,009,771 B1
- Document ID: US12009771B1
- Status: Granted
- Kind: B1
- Application number: 18/178,207
- Filed: 2023-03-03
- Granted: 2024-06-11
- Earliest claimed: 2023-03-03
- Assignees: King Fahd University of Petroleum and Minerals
- Applicants: King Fahd University of Petroleum and Minerals
- Inventors: Muhammad Khalid; Mohammad Ali
- Web page: https://patentgrep.com/patent/US12009771B1

## CPC

- H02P 9/007: {Control circuits for doubly fed generators}
- H02J 3/381: {Dispersed generators}
- H02J 2101/28: Wind energy
- H02P 2101/15: for wind-driven turbines
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY

## Abstract

A doubly fed induction generator (DFIG) speed control system is provided. The system includes a wind turbine and a wound rotor induction generator connected to the wind turbine through a drive train system and to a power grid. The system further includes a back-to-back voltage source converter (VSC) with a rotor side converter (RSC) and a grid side converter (GSC). The RSC is connected to the wound rotor induction generator and the GSC is connected to the power grid. A wind profile sensor measures a wind profile and a VSC controller provides control to the RSC and the GSC. The VSC controller applies a nonsingular fast terminal sliding mode control (NSFTSMC) scheme at the RSC at least partially based on the received wind profile to stabilize a rotor speed of the wound rotor induction generator.

## Claims

### Claim 1

A doubly fed induction generator (DFIG) speed control system, comprising:
a wind turbine;
a wound rotor induction generator configured to connect with the wind turbine through a drive train system;
the wound rotor induction generator is further configured to connect to a power grid;
a back-to-back voltage source converter (VSC) with a rotor side converter (RSC) and a grid side converter (GSC), wherein the RSC is connected to the wound rotor induction generator and the GSC is connected to the power grid;
a wind profile sensor configured to measure a wind profile; and
a VSC controller configured to provide control to the RSC and the GSC;
wherein the VSC controller is configured to apply a nonsingular fast terminal sliding mode control (NSFTSMC) scheme at the RSC at least partially based on the received wind profile to stabilize a rotor speed of the wound rotor induction generator to a base speed and to achieve a shorter stabilizing time than a conventional proportional integral controller;
wherein the nonsingular fast terminal sliding mode control (NSFTSMC) scheme is expressed as:
u
=
-
a
1
b
⁢
x
2
-
❘
"\[LeftBracketingBar]"
x
2
❘
"\[RightBracketingBar]"
2
-
ξ
2
⁢
sign
(
x
2
)
b
⁢
c
2
⁢
ζ
2
⁢
(
x
2
+
c
1
⁢
ξ
1
⁢
❘
"\[LeftBracketingBar]"
x
1
❘
"\[RightBracketingBar]"
ξ
1
-
1
⁢
x
2
)
-
α
1
⁢
s
-
α
2
⁢
❘
"\[LeftBracketingBar]"
s
❘
"\[RightBracketingBar]"
β
⁢
sign
(
s
)
,
where u is the control input,
a
1
=
-
B
J
,
b
=
k
t
⁢
k
1
J
,
where B is the friction coefficient, J is the moment of inertia, kt and k1 are gain constants, α1>0, α2>0, and β∈(0,1) is the pitch angle;
x1 is a first order mechanical dynamic equation x1=θ*r−θr where θ*r is the desired angular position and θr is the angular position of the wind turbine;
x2 is a second order mechanical dynamic equation
x
2
=
-
(
T
e
-
T
L
)
⁢
1
Js
+
B
where TL is the disturbance load torque and Te is the electromechanical control torque; and
s is the nonsingular fast terminal sliding surface (NSFTSS) expressed as:
s=x1+c1|x1|ξ1 sign(x1)+c2|x2|ξ2 sign(x2),
where c1 and c2 are positive coefficients of NSFTSS s∈ and ξ1 and ξ2 are the auxiliary state variables of observer where ξ2∈(1, 2) and ξ1>ξ2.

### Claim 2 (depends on 1)

The system of claim 1, wherein the drive train system comprises:
a low-speed shaft;
a high-speed shaft; and
a gearbox.

### Claim 3 (depends on 1)

The system of claim 1, wherein the RSC is an AC-to-DC converter and the GSC is a DC-to-AC converter.

### Claim 4 (depends on 1)

The system of claim 1, wherein the base speed is 1.2 times a synchronous speed of the wound rotor induction generator.

### Claim 5 (depends on 1)

The system of claim 1, wherein the measured wind profile includes at least a wind speed.

### Claim 6

A method for controlling a doubly fed induction generator (DFIG) speed control system, comprising:
measuring a wind profile; and
applying a nonsingular fast terminal sliding mode control (NSFTSMC) scheme to the DFIG speed control system, the DFIG speed control system is configured to include:
a wind turbine;
a wound rotor induction generator configured to connect with the wind turbine through a drive train system and connect to a power grid;
a back-to-back voltage source converter (VSC) with a rotor side converter (RSC) and a grid side converter (GSC), wherein the RSC is connected to the wound rotor induction generator and the GSC is connected to the power grid; and
a VSC controller;
wherein the NSFTSMC scheme is applied to stabilize a rotor speed of the wound rotor induction generator to a base speed and to achieve a shorter stabilizing time than a conventional proportional integral controller;
wherein the nonsingular fast terminal sliding mode control (NSFTSMC) scheme is expressed as:
u
=
-
a
1
b
⁢
x
2
-
❘
"\[LeftBracketingBar]"
x
2
❘
"\[RightBracketingBar]"
2
-
ξ
2
⁢
sign
(
x
2
)
b
⁢
c
2
⁢
ξ
2
⁢
(
x
2
+
c
1
⁢
ξ
1
⁢
❘
"\[LeftBracketingBar]"
x
1
❘
"\[RightBracketingBar]"
ξ
1
-
1
⁢
x
2
)
-
α
1
⁢
s
-
α
2
⁢
❘
"\[LeftBracketingBar]"
s
❘
"\[RightBracketingBar]"
β
⁢
sign
(
s
)
,
where u is the control input
a
1
=
-
B
J
,
b
=
k
t
⁢
k
1
J
,
where B is the friction coefficient, J is the moment of inertia, kt and k1 are gain constants, α1>0, α2>0, and β∈(0,1) is the pitch angle;
x1 is a first order mechanical dynamic equation x1=θ*r−θr where θ*r is the desired angular position and θr is the angular position of the wind turbine;
x2 is a second order mechanical dynamic equation
x
2
=
-
(
T
e
-
T
L
)
⁢
1
Js
+
B
where TL is the disturbance load torque and Te is the electromechanical control torque; and
s is the nonsingular fast terminal sliding surface (NSFTSS) expressed as:
s=x1+c1|x1|ξ1 sign(x1)+c2|x2|ξ2 sign(x2),
where c1 and c2 are positive coefficients of NSFTSS s∈ and ξ1 and ξ2 are the auxiliary state variables of observer where ξ2∈(1, 2) and ξ1>ξ2.

### Claim 7 (depends on 6)

The method of claim 6, wherein the base speed is 1.2 times a synchronous speed of the wound rotor induction generator.

### Claim 8 (depends on 6)

The method of claim 6, further comprises:
applying an electrical control scheme to the GSC; and
applying a rotor blade control scheme to the wind turbine to control a pitch of rotor blades of the wind turbine.

### Claim 9 (depends on 6)

The method of claim 6, wherein the drive train system in the DFIG based wind turbine further comprises:
a low-speed shaft;
a high-speed shaft; and
a gearbox.

### Claim 10 (depends on 6)

The method of claim 6, wherein the RSC is an AC-to-DC converter.

### Claim 11 (depends on 6)

The method of claim 6, wherein the GSC is a DC-to-AC converter.

### Claim 12 (depends on 6)

The method of claim 6, wherein the received wind profile includes at least a wind speed.

### Claim 13

A method for controlling a doubly fed induction generator (DFIG) speed control system, comprising:
measuring a wind profile; and
applying a nonsingular fast terminal sliding mode control (NSFTSMC) scheme to stabilize a rotor speed of the DFIG to a base speed and to achieve a shorter stabilizing time than a conventional proportional integral controller, wherein the NSFTSMC scheme is expressed as:
u
=
-
a
1
b
⁢
x
2
-
❘
"\[LeftBracketingBar]"
x
2
❘
"\[RightBracketingBar]"
2
-
ξ
2
⁢
sign
(
x
2
)
b
⁢
c
2
⁢
ξ
2
⁢
(
x
2
+
c
1
⁢
ξ
1
⁢
❘
"\[LeftBracketingBar]"
x
1
❘
"\[RightBracketingBar]"
ξ
1
-
1
⁢
x
2
)
-
α
1
⁢
s
-
α
2
⁢
❘
"\[LeftBracketingBar]"
s
❘
"\[RightBracketingBar]"
β
⁢
sign
(
s
)
,
where u is the control input,
a
1
=
-
B
J
,
b
=
k
t
⁢
k
1
J
,
where B is the friction coefficient, J is the moment of inertia, kt and k1 are gain constants, α1>0, α2>0, and β∈(0,1) is the pitch angle;
x1 is a first order mechanical dynamic equation x1=θ*r−θr where θ*r is the desired angular position and θr is the angular position of the wind turbine;
x2 is a second order mechanical dynamic equation
x
2
=
-
(
T
e
-
T
L
)
⁢
1
Js
+
B
where TL is the disturbance load torque and Te is the electromechanical control torque; and
s is the nonsingular fast terminal sliding surface (NSFTSS) expressed as:
s=x1+c1|x1|ξ1 sign(x1)+c2|x2|ξ2 sign(x2),
where c1 and c2 are positive coefficients of NSFTSS s∈, and ξ1 and ξ2 are the auxiliary state variables of observer where ξ2∈(1, 2) and ξ1>ξ2.

### Claim 14 (depends on 13)

The method of claim 13, wherein the DFIG speed control system is configured to include:
a wind turbine including a low-speed shaft, a high-speed shaft, and a gearbox;
a wound rotor induction generator configured to connect with the wind turbine through a drive train system and connect to a power grid;
a back-to-back voltage source converter (VSC) with a rotor side converter (RSC) and a grid side converter (GSC), wherein the RSC is connected to the wound rotor induction generator and the GSC is connected to the power grid; and
a VSC controller.

### Claim 15 (depends on 14)

The method of claim 14, wherein applying the NSFTSMC scheme is done by the VSC controller to the RSC.

### Claim 16 (depends on 14)

The method of claim 14, wherein the RSC is an AC-to-DC converter and the GSC is a DC-to-AC converter.

### Claim 17 (depends on 13)

The method of claim 13, wherein the base speed is 1.2 times a synchronous speed of the wound rotor induction generator.

### Claim 18 (depends on 13)

The method of claim 13, wherein the measured wind profile includes at least a wind speed.