disturbance and adapting parameter variations and model un-
certainties. Thus a robust and adaptive current controller based on
generalized predictive control with sliding mode disturbance
compensation is proposed in this paper.
3.1. The design of predictive current controller
Inspired by the generalized predictive control theory in [27],
the design of current controller for ideal system is presented as
follows.
According to (4), neglecting the disturbance part, the nominal
model can be expressed as
=()+()
=()=()
()
xfxgxu
yhxgxx
,
,
5
1
1
2
where
=[ ]uuu
dq
T
111
.
Let
i
d
,
i
q
be the reference current, and
=[
**
]yii
r
dq
. First of all,
the cost function is defined as
∫
τττττ
=(
^
(+)−
^
(+))(
^
(+)−
^
(+))
()
J ytytytytd
1
2
,
6
o
T
r
T
r
where T is the predictive horizon,
τ
^
(+
yt
and
τ
^
(+
yt
r
represent
the predictive current and the predictive reference current,
respectively.
According to the nominal PMSM system (5), each of the output
current has the same relative degree
= 1
. The total relative de-
gree of the system is equal to the systems order. Consequently,
there is no zero dynamics. The output current is measurable. In
addition, the current is taken as the smooth variable, so it satisfies
continuously differentiable with respect to the time. Therefore,
four assumptions given in [27] can be satisfied. In order to alleviate
the computation burden, the control order
=r
is chosen, thus
the control input
τ(+
ut
in the moving time frame is constant.
Repeated differentiation up to
ρ(+
r
th of the output
^
(
yt
with
respect to time
^
()= ()
^
()= ()+ ()
()
yt Lhx
yt Lhx Lhxu
,
,
7
f
fg
0
11
1
1
where
()= ()=[ ]Lhx hx i i
fdq
T0
,
()= ()= (
∂( ( ))
∂
Lhx f x f x
f
hx
x
1
,
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
()=
∂( ( ))
∂
()=Lhx
hx
x
gx
0
0
.
g
L
L
1
1
1
1
d
q
1
Because
= 1
and
=r
, at least
+=r 1
terms should be
maintained in the truncated Taylor's expansion of
τ
^
(+
yt
, i.e.
ττ
^
(+)=
^
()+
^
() =
()
yt yt y tm,1,2.
8
mmm
where m is defined as an element index of multidimensional
output
^
(
yt
, with
^
()=[
^
()
^
()] =[ ]yt y t y t i i
T
dq
12
.
Then
⎡
⎣
⎢
⎤
⎦
⎥
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
τ
τ
τ
^
(+)=
^
()
^
()
()
yt
yt
yt
10 0
010
.
9
Let
⎡
⎣
⎢
⎤
⎦
⎥
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
Γτ
τ
τ
()=
¯
()=
^
()
^
()
()
Yt
yt
yt
10 0
010
,.
10
It follows that
τΓτ
^
(+)= ()
¯
()
()
yt Yt.
11
Similarly, the Taylor's expansion of the reference output current
is
τΓτ
^
(+)= ()
¯
()
()
yt Yt,
12
r
r
where
¯
()=[ ()
()]
tytyt
r
r
T
r
TT
and
(
yt
r
is the derivative of the re-
ference current.
Let
∫
ΓΓτΓττ
¯
()= ()()Td
T
T
0
, and according to the Appendix A in
[27], the
(
ij,
th element in the matrix
Γ
¯
()T
can be represented as
⎡
⎣
⎢
⎤
⎦
⎥
Γ
¯
() =
( − )!( − )!( + − )
=
()
+−
T
ijij
T
T
ij
1
11 1
0
0
, , 1, 2.
13
ij
ij
,
1
Then, allow for the truncation of
τ
^
(+
yt
and
τ
^
(+
yt
r
, the cost
function is approximatively equal to
Γ
=[
¯
()−
¯
()]
¯
()[
¯
()−
¯
()]
()
JYtYtTYtYt
1
2
.
14
r
T
r
To minimize the current tracking error in finite horizon, the
generalized predictive control law [18] for PMSM is derived as
=− ()( + ()−
)
()
ρ
−
uGxKMLhxy,
15
f
r
1
11
where
⎡
⎣
⎤
⎦
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
⎡
⎣
⎤
⎦
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
()=
() ()
==
()− ()
=
−
*
−
*
ρ
Gx
LhxLhx
M
hx y t
ii
ii
0
0
,,
gg
L
L
r
dd
qq
11
1
12
1
1
1
d
q
g,
11 12
represent the column vector of
(
x
1
.
∈
×
KR
2
is the first
2 rows of the matrix
Γ
¯
−
rr
1
Γ
¯
ρ
T
, and
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
Γ
ΓΓ
ΓΓ
¯
()=
¯¯
¯¯
ρρ ρ
ρ
T ,
r
r
T
rr
where
Γ
¯
∈
ρρ
×
R
22
,
Γ
¯
∈
ρ
×
R
r
2
,
Γ
¯
∈
×
R
rr
22
. Then, K can be get as
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
=K
0
0
.
T
T
3
2
3
2
The control laws
u
d1
and
u
q1
calculated in (15) are the reference
voltage in the PMSM control system based on GPC. It's worth
noting that the controller in (15) can solve the GPC control pro-
blem in general without any additional supporting means, and the
influence triggered by model uncertainties in the PMSM drive
system is disregarded. The current regulator performance may be
affected significantly by the strong disturbance. For this reason, it's
necessary to consider the disturbance to strength the robustness
of the current controller.
3.2. The design of sliding mode disturbance compensation controller
To improve the robustness of the current controller and guar-
antee the fast current response, a sliding mode disturbance com-
pensation [32,33] combining the generalized predictive controller
is studied. The objective is to find a control voltage u such that the
trajectories of the real motor system (4) coincide with the nominal
system (5). A kind of method is to add another control
=[ ]uuu
dq
222
to the control
u
1
of the nominal system, i.e.
=+uu u
12
. The structure of the proposed current controller is
shown in Fig. 1. The sliding mode control
u
will be used to
eliminate the disturbance d, and the predictive control
u
1
provides
the preliminaries for the design of sliding mode controller.
u
is a
discontinuous control. According to (4) and (5) yields
() =−
()
gxu d,
16
eq
1
2
where
u
eq2
is the equivalent control of
u
.
X. Liu et al. / ISA Transactions 71 (2017) 542–552544