Method of designing a static synchronous compensator based on passivity-based control
This invention presents a method of novel nonlinear control for designing Static Synchronous Compensators (STATCOM). A passivity-based approach is proposed for designing robust nonlinear STATCOM controller. The mathematical model of STATCOM will be represented by an Euler-Lagrange (EL) system corresponding to a set of EL parameters. By employing the Park's transformation, the differential geometry approach is used to investigate the power system dynamics with considering STATCOM under the synchronous d-q frame. The energy-dissipative properties of the proposed model derived in the synchronous d-q rotating frame are fully retained. This model also consider the dynamic response of the changable load. Finally, the passivity-based control is employed by using energy shaping and damping injection techniques to produce the proper control signals for Voltage Source Converter. So that the system embedded with STATCOM is more robust and stable.
1. A method for controlling current, in an electric power system based on passivity-based control theory, to regulate a load bus voltage with a static synchronous compensator (STATCOM) controller designed using a STATCOM model, comprising:
constructing a STATCOM model with a viewpoint of energy balancing as a circuit model constructed in Euler-Lagrange (EL) dynamic frame, wherein the model also considers the dynamic response of a changeable load, and is used to determine a control command for fast adjustment of a load characteristic in an electric power system using a STATCOM controller wherein the STATCOM model is given by
Dż−M{dot over (w)}+Rz+J ( u ) z−R 1 w+J 1 ( u ) w=ε,
where
z
=
[
i
sd
i
sq
V
dc
]
,
w
=
[
i
Ld
i
Lq
0
]
,
M
=
[
L
0
0
0
L
0
0
0
0
]
,
J
1
(
u
)
=
[
0
-
ω
L
0
ω
L
0
0
-
1.5
u
d
-
1.5
u
q
0
]
,
R
1
=
[
R
0
0
0
R
0
0
0
0
]
,
L=the Lagrangian term of the STATCOM EL model, D,M =the Rayleigh disruptive term of the STATCOM EL model, R,R l =the dissipation term of the STATCOM EL model, J,J l =the interconnection term of the STATCOM EL model, ω=dθ/dt=the angular speed of the ac system, θ=the angle of the STATCOM bus voltage, ε=the external force term of the STATCOM EL model, i sd ,i sq =the d-q axis current through a loss resistor ( 114 ) and a loss inductor ( 115 ) under the direct-quadrature rotating frame, i Ld ,i Lq =the d-q axis current through the changeable load under the direct-quadrature rotating frame, V dc =the DC side voltage across a coupling capacitor ( 113 ) and the loss resistor, u d ,u q =the d-q axis control input of converter ( 106 );
designing a STATCOM controller for controlling current in said electric power system on the basis of passivity-based control using said STATCOM model and technologies of energy shaping and damping injection and using controlled current to regulate a load bus voltage; wherein said damping injection changes the STATCOM model to Dż*−M{dot over (w)}+Rz*+J(u)z*−R 1 w+J 1 (u)w−R m {tilde over (z)}=ε,
where
R
m
=
[
R
m
1
0
0
0
R
m
2
0
0
0
R
m
3
-
1
]
,
and wherein the energy shaping error signal is defined as {tilde over (z)}=z−z*=[i sd −i* sd i sq −i* sq V dc −V* dc ] T ; and
controlling current in said electric power system on the basis of passivity-based control to regulate the load bus voltage with the STATCOM controller.
2. The method of claim 1 , wherein the designed static synchronous compensator uses direct-quadrature-axis current in the EL model to fast regulate the load bus voltage and STATCOM DC voltage.
3. The method of claim 1 , wherein three steps of designing the STATCOM are EL model construction, energy shaping, and damping injection.
4. The method of claim 1 , wherein the dynamic model of STATCOM is based on the concept of energy balancing so that the Euler-Lagrangian (EL) dynamic model of STATCOM is formed, including a feature of nonlinearity of an original system, and wherein a switching loss of converter ( 106 ) and the changeable load are also considered.
5. The method of claim 3 , wherein in energy shaping, the energy of the electric power system is corrected for a set of minimum potential energy at a default balance point, an oriented error signal, and a new energy function.
6. The method of claim 3 , wherein in damping injection, the asymptotic stability of the electric power system is enhanced.