# US 12,119,659 B2 · Hybrid microgrid system for wind power electrical generation

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- Number: US 12,119,659 B2
- Document ID: US12119659B2
- Status: Granted
- Kind: B2
- Application number: 18/620,141
- Filed: 2024-03-28
- Published: 2024-08-22
- Granted: 2024-10-15
- Earliest claimed: 2022-10-27
- Assignees: King Fahd University of Petroleum and Minerals
- Applicants: King Fahd University of Petroleum and Minerals
- Inventors: Muhammad Khalid; Muhammad Maaruf
- Web page: https://patentgrep.com/patent/US12119659B2

## CPC

- H02J 3/381: {Dispersed generators}
- H02J 3/32: using batteries or super capacitors with converting means
- H02M 1/10: Arrangements incorporating converting means for enabling loads to be operated at will from different kinds of power supplies, e.g. from AC or DC
- H02M 3/1582: {Buck-boost converters (H02M3/1584 takes precedence)}
- H02M 5/4585: {having a rectifier with controlled elements}
- H02J 2101/24: Photovoltaics
- H02J 2101/28: Wind energy
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)

## Abstract

A system and a method for controlling a hybrid microgrid system (HMS) is disclosed. The HMS includes a WTG, an RSC, a GSC, a DC-link connecting the RSC and the GSC, a PV system that outputs a DC current to the DC-link, a rechargeable battery, a bidirectional BBC connected between the DC-link and the rechargeable battery, and a controller. The method for controlling the HMS includes: preparing a definition set including a characteristic element ci and equations defining desired value ci*, a fractional order sliding mode surface ζi, and a control law element uicnt; monitoring ci(t) and the HMS status; calculating the equations based on monitored information; and controlling the HMS based on the uicnt(t) calculated and in accordance with a global sliding mode control with fractional order terms. The ζi comprises a fractional time integral and fractional time derivative of ei(t), where ei(t)=ci(t)−ci*(t). The uicnt(t) satisfies ζ i ( t ) ⁢ d ⁢ ζ i ( t ) dt < 0 , when ζi(t)≠0.

## Claims

### Claim 1

A hybrid microgrid system (HMS) for wind power electrical generation comprising:
a wind turbine (WT) and an electric generator;
a grid side converter (GSC) configured to output a power to a point of common coupling (PCC);
a DC-link configured to receive a power from the WT and the electric generator and to supply a power to the GSC;
a rechargeable battery configured to exchange a power between the DC-link;
a load configured to receive a power via the PCC;
a utility grid configured to exchange power via the PCC; and
a controller comprising: a processor; a memory; a bus-line; and I/O port,
wherein, the controller is configured to control the HMS by executing a program installed in the memory and in accordance with a global sliding mode control with fractional order terms (GSMCFO) method, and wherein, the program comprises a definition set customized for the HMS and to be referred in applying the GSMCFO method to the HMS,
wherein the definition set comprises: a characteristic element ci to be measured; and equations defining a desired value ci* of the characteristic element ci, a fractional order sliding mode (FOSM) surface (i of the characteristic element ci, and a control law element uicnt of the characteristic element ci, and
wherein the controller is further configured to
monitor the characteristic element ci(t) and a related status of the HMS,
calculate at least one of the equations defined in the definition set based on the characteristic element ci(t) monitored and the status of the HMS monitored, and
control the HMS based on the control law element uicnt(t) calculated,
wherein the equation defining the FOSM surface ζi(t) for the characteristic element ci(t) comprises a fractional time integral of a tracking error ei(t) and a fractional time derivative of the tracking error ei(t), wherein the tracking error ei (t) for the characteristic element ci(t) is defined as,
ei(t)=ci(t)−ci*(t),
wherein the equation defining the control law element uicnt(t) is configured to satisfy a condition
ζ
i
(
t
)
⁢
d
⁢
ζ
i
(
t
)
dt
<
0
,
so far as ζi(t) is not zero.

### Claim 2 (depends on 1)

The hybrid microgrid system of claim 1, wherein the definition set further comprises: a minimum value SOCmin in and a maximum value SOCmax of the state of charge (SOC) of the rechargeable battery; and equations defining a power imbalance ΔP and a power balance condition of the HMS, given respectively as,
ΔP=Pre+Pug−Pdem−Pb
ΔP=0,
wherein Pre represents a total power generated by the WT and the electric generator, Pug, a grid power exchanged between the utility grid and the PCC, Pdem, a load demand, Pb, a battery power exchanged between the rechargeable battery and the DC-link,
wherein the controller is further configured to
monitor elements required to calculate a power imbalance ΔP and a SOC,
calculate a power imbalance ΔP with the equation given in the definition set, and
control the battery power Pb and the grid power Pug to satisfy and maintain the power balance condition, under a restriction that the SOC of the rechargeable battery satisfies a condition,
SOCmin≤SOC≤SOCmax.

### Claim 3 (depends on 2)

The hybrid microgrid system of claim 2, wherein the WT comprises:
a wind turbine generator and the electric generator comprises a rotor and a stator;
a rotor side converter (RSC) configured to receive an AC power from the electric generator and output an RSC output DC current to the DC-link;
a solar photovoltaic (PV) system configured to output a PV output DC current to the DC-link; and
a bidirectional buck-boost converter (BBBC) connected between the DC-link and the rechargeable battery and configured to control a power exchanged between the rechargeable battery and the DC-link,
and wherein, the definition set further comprises an equation defining an equivalent control law element uieqv for the characteristic element ci, wherein the equivalent control law element uieqv comprises a maximum disturbance term Rt1−μ δi, representing a possible maximum value of a lumped external disturbances and parametric perturbations to the tracking error ei(t), wherein, Rt1−μ represents a Riemann-Liouville fractional integration, and δi, a positive function,
wherein, the equation defining the control law element uicnt(t) comprises a function SG (ζi(t)) given by a signum function sgn(ζi(t)) or one of its smooth approximations including
tan
⁢
h
⁢
(
ζ
i
(
t
)
θ
)
,
wherein, θ(>0).

### Claim 4 (depends on 3)

The hybrid microgrid system of claim 3, wherein the characteristic element c1 is an angular frequency ωr of the WT, and the characteristic element c2 is a d-axis stator current Ids, wherein the desired value ωr* for the angular frequency ωr of the WT is defined as,
c
1
*
(
t
)
=
ω
r
*
=
λ
*
⁢
V
w
R
,
wherein λ* denotes a desired tip speed ratio, giving a maximum power coefficient for the turbine with a blade radius R, at a wind speed Vw,
wherein the desired value Ids* for the d-axis stator current Ids of the rotor is given as,
c2*(t)=Ids=0
wherein the equations defining the FOSM surfaces ζi(t) for the characteristic elements c1(i=1, 2) are given as,
ζ1(t)=k1Rtμe1(t)+σ1Rt1-μe1(t)+Rt2-μe1(t),
ζ2(t)=k2Rtμe2(t)+Rt1-μe2(t)
wherein, 0<μ<1, k1, k2, and σ1 are positive constants, Rtμ denotes a Riemann-Liouville fractional integration, Rt1-μ and Rt2-μ denote Riemann-Liouville fractional derivations,
wherein the equivalent control law element u1eqv(t) and the control law element uicnt(t) of the angular frequency ωr are given by q-axis stator voltages Vqseqv(t) and Vqscnt(t), and defined respectively as,
u
1
eqv
(
t
)
=
V
qs
eqv
(
t
)
=
-
1
a
⁢
(
k
1
⁢
e
1
(
t
)
+
σ
1
⁢
e
.
1
(
t
)
+
R
t
1
-
μ
⁢
δ
1
-
ω
¨
r
*
+
a
[
L
q
⁢
ω
r
⁢
I
ds
+
R
s
⁢
I
qs
+
λ
r
⁢
ω
r
]
)
,
u
1
cnt
(
t
)
=
V
qs
cnt
(
t
)
=
V
qs
eqv
(
t
)
-
1
a
[
ϱ
1
⁢
R
t
1
-
μ
⁢
SG
⁡
(
ζ
1
(
t
)
)
⁢
❘
"\[LeftBracketingBar]"
ζ
1
(
t
)
❘
"\[RightBracketingBar]"
α
+
γ
1
⁢
R
t
1
-
μ
⁢
ζ
1
(
t
)
]
,
wherein the equivalent control law element u2eqv(t) and the control law element u2cnt(t) of the d-axis stator current Ids of the rotor are given by d-axis stator voltages Vds eqv(t) and Vdscnt(t), and defined respectively as
u
2
eqv
(
t
)
=
V
ds
eqv
(
t
)
=
-
L
d
(
k
2
⁢
e
2
(
t
)
+
[
L
q
⁢
ω
r
⁢
I
qs
-
R
s
⁢
I
ds
]
L
d
+
R
t
1
-
μ
⁢
δ
2
-
I
.
ds
*
)
,
u
2
cnt
(
t
)
=
V
ds
cnt
(
t
)
=
V
ds
eqv
(
t
)
-
L
d
[
ϱ
1
⁢
R
t
1
-
μ
⁢
SG
⁡
(
ζ
2
(
t
)
)
⁢
❘
"\[LeftBracketingBar]"
ζ
2
(
t
)
❘
"\[RightBracketingBar]"
α
+
γ
2
⁢
R
t
1
-
μ
⁢
ζ
2
(
t
)
]
,
wherein α is given by
a
=
3
⁢
P
2
⁢
Ar
2
⁢
JL
q
,
wherein P denotes a number of pole pairs of the rotor, Λr, a rotor flux, J, an inertia of mechanical shaft of the wind turbine generator, Lq, a q-axis self-inductance of the stator, Rs, a stator resistance, Iqs, a q-axis stator current, Λr, a rotor flux, Ld, a d-axis self-inductance of the stator, Rt1-μδ1 and Rt1-μδ2 represent the maximum disturbance terms, α ∈ (0, 1), i and γi(i=1, 2) are positive constants.

### Claim 5 (depends on 3)

The hybrid microgrid system of claim 3, wherein the DC-link further comprises a DC-bus and a DC-link capacitor, and wherein the characteristic element c3 is a DC-link voltage Vdc,
the desired value Vdc* defined for the DC-link voltage Vdc is given as
c
3
*
(
t
)
=
V
dc
*
=
{
V
pv
MPPT
;
when
⁢
V
dc
min
≤
V
pv
MPPT
≤
V
dc
max
,
V
dc
nom
;
when
⁢
V
pv
MPPT
<
V
dc
min
,
or
⁢
V
pv
MPPT
>
V
dc
max
,
wherein VpvMPPT represents an output voltage of the PV system under a maximum power point tracking (MPPT) operation, Vdcmin, Vdcmax and Vdcnom represent a minimum allowable value, a maximum allowable value, and a nominal value of the DC-link voltages, each predetermined respectively,
the equation defining the FOSM surfaces ζ3(t) of the DC-link voltage is given as,
ζ3(t)=k3Rtμe3(t)+Rt1-μe3(t)
wherein, μ ∈ (0, 1) and k3 are positive constants, Rt1-μ denotes a Riemann-Liouville fractional integration, Rt1-μ denotes a Riemann-Liouville fractional derivation,
wherein the equations defining the equivalent control law element u3eqv(t) and the control law element u3cnt(t) of the DC-link voltage Vdc are given by d-axis AC output currents Ideqv(t) and Idcnt(t) from the GSC, and defined respectively as,
u
3
eqv
(
t
)
=
I
d
eqv
(
t
)
=
2
3
⁢
C
dc
⁢
V
dc
V
d
⁢
(
k
3
⁢
e
3
(
t
)
+
P
w
C
dc
⁢
V
dc
+
I
pv
C
dc
+
(
1
-
D
)
C
dc
⁢
I
b
+
R
t
1
-
μ
⁢
δ
3
-
V
.
dc
*
(
t
)
)
,
u
3
cnt
(
t
)
=
I
d
cnt
(
t
)
=
I
d
eqv
(
t
)
+
2
3
[
ϱ
3
⁢
R
t
1
-
μ
⁢
SG
⁡
(
ζ
3
(
t
)
)
⁢
❘
"\[LeftBracketingBar]"
ζ
3
(
t
)
❘
"\[RightBracketingBar]"
α
+
γ
3
⁢
R
t
1
-
μ
⁢
ζ
3
(
t
)
]
,
wherein Cdc denotes a capacitance of the DC-link capacitor, Vd, a voltage of the AC output from the GSC, Pw, an output power from the RSC, Ipv, an output current from the PV system, D, a duty cycle ratio of the BBBC, Ib, a battery output current, Rt1-μδ3 is the maximum disturbance term, α ∈ (0, 1), 3 and γ3 are positive constants.

### Claim 6 (depends on 3)

The hybrid microgrid system of claim 3, wherein the GSC is further configured to output an AC output to a point of common coupling (PCC) via a grid side filter,
wherein the characteristic elements ci(t) (i=4, 5) are a d-axis AC current Id (i=4) of the AC output from the GSC, and a q-axis AC current Iq (i=5) of the AC output from the GSC for, respectively,
the desired values defined for the d-axis AC current and the q-axis AC current are given respectively as
c
4
*
(
t
)
=
I
d
*
=
I
d
=
2
3
⁢
P
dem
-
P
ug
V
d
,
c5*(t)=Iq*=0,
wherein Pdem and Pug represent a power demand at the load and a power exchanged between the PCC and the utility grid, respectively, wherein Pug>0, when provided from the utility grid to the PCC, Pug<0, when provided from the GSC to the utility grid, Vd, a d-axis AC voltage of the AC output from the GSC,
the equations defining the FOSM surfaces ζi(t) for the d-axis AC current Id (i=4) and the q-axis AC current Iq (i=5) are given respectively as,
ζ4=k4Rtμe4(t)+Rt1-μe4(t),
ζ5(t)=k5Rtμe4(t)+Rt1-μe5(t),
wherein μ ∈ (0, 1), k4, and k5 are positive constants, Rtμ and Rt1-μ each denotes a Riemann-Liouville fractional integration and a Riemann-Liouville fractional derivation, respectively,
wherein the equations defining the equivalent control law element u4eqv(t) and the control law element u4cnt(t) of the d-axis AC current Id are given by d-axis AC voltages Vd eqv(t) and Vdcnt(t) of the AC output from the GSC, and defined respectively as,
u
4
eqv
(
t
)
=
V
d
eqv
(
t
)
=
-
L
f
(
k
4
⁢
e
4
(
t
)
-
I
.
d
*
-
1
L
f
[
R
f
⁢
I
d
+
U
d
-
L
f
⁢
ω
g
⁢
I
q
-
R
t
1
-
μ
⁢
δ
4
]
)
,
u
4
cnt
(
t
)
=
V
d
cnt
(
t
)
=
V
d
eqv
(
t
)
-
L
f
[
ϱ
4
⁢
R
t
1
-
μ
⁢
SW
⁡
(
ζ
4
(
t
)
)
⁢
❘
"\[LeftBracketingBar]"
ζ
4
(
t
)
❘
"\[RightBracketingBar]"
α
+
γ
4
⁢
R
t
1
-
μ
⁢
ζ
4
(
t
)
]
,
wherein the equations defining the equivalent control law element u5eqv(t) and the control law element u5cnt(t) of the q-axis AC current Iq are given by q-axis AC voltages Vqeqv(t) and Vqcnt(t) of the AC output from the GSC, and defined respectively as,
u
5
eqv
(
t
)
=
V
d
eqv
(
t
)
=
-
L
f
(
k
5
⁢
e
5
(
t
)
-
I
.
d
*
-
1
L
f
[
R
f
⁢
I
d
+
U
d
-
L
f
⁢
ω
g
⁢
I
q
-
R
t
1
-
μ
⁢
δ
5
]
)
,
u
5
cnt
(
t
)
=
V
d
cnt
(
t
)
=
V
d
eqv
(
t
)
-
L
f
[
ϱ
5
⁢
R
t
1
-
μ
⁢
SW
⁡
(
ζ
5
(
t
)
)
⁢
❘
"\[LeftBracketingBar]"
ζ
5
(
t
)
❘
"\[RightBracketingBar]"
α
+
γ
5
⁢
R
t
1
-
μ
⁢
ζ
5
(
t
)
]
,
wherein Lf and Rf denote a grid side filter inductance and a grid side filter resistance, respectively, Ud and Uq, a d-axis and a q-axis voltages at a point of common coupling (PCC), respectively, ωg, an electrical angular frequency of the AC output from the GSC, Rt1-μδi,(i=4, 5) are the maximum disturbance terms, α ∈ (0, 1), i and γi(i=4, 5) are positive constants.

### Claim 7 (depends on 3)

The HMS of claim 3, wherein the BBBC is configured to facilitate charging of the rechargeable battery while operating as a buck converter, and to facilitate discharging to the DC-link while operating as a boost converter,
and wherein the characteristic element c1(i=6) is a battery current Ib,
the desired value Ib* defined for the battery current Ib is given as,
c
6
*
(
t
)
=
I
d
*
=
I
d
=
2
3
⁢
P
dem
-
P
ug
V
d
,
wherein Pre represents a sum of powers generated by the WT, Pug a power supplied by the utility grid, Pdem, a load demand, and Vb, a battery voltage,
the equation defining the FOSM surfaces ζ6(t) of the battery current is given as,
ζ6(t)=k6Rt1-μe6+Rt1-μe6,
wherein, μ ∈ (0, 1) and k6 are positive constants, Rt1-μ denotes a Riemann-Liouville fractional integration, Rt1-μ denotes a Riemann-Liouville fractional derivation,
wherein the equations defining the equivalent control law element u6eqv(t) and the control law element u6cnt(t) of the battery current Ib are given by duty cycles Deqv(t) and Dcnt(t) of the BBBC, and defined respectively as,
u
6
eqv
(
t
)
=
D
eqv
(
t
)
=
L
b
V
dc
⁢
(
k
6
⁢
e
6
(
t
)
+
V
b
L
b
-
I
b
⁢
R
b
L
b
+
R
t
1
-
μ
⁢
δ
6
-
I
b
*
)
,
u
6
cnt
(
t
)
=
D
cnt
(
t
)
=
D
eqv
(
t
)
-
L
b
[
ϱ
6
⁢
R
t
1
-
μ
⁢
SG
⁡
(
ζ
6
(
t
)
)
⁢
❘
"\[LeftBracketingBar]"
ζ
6
(
t
)
❘
"\[RightBracketingBar]"
α
+
γ
6
⁢
R
t
1
-
μ
⁢
ζ
6
(
t
)
]
,
wherein Lb denotes a battery inductance, Vb, a battery voltage, Rb, a battery resistance, Vdc, a DC-link voltage, Rt1-μδ6 represents the maximum disturbance term, α ∈ (0, 1), 6 and γ6 are positive constants.