1336 IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS, VOL. 5, NO. 3, SEPTEMBER 2017
Fig. 1. Schematic of vector controlled PMSM drive system.
analysis are given in Section IV. Finally, conclusions are
summarized in Section V.
II. PMSM M
ODEL AND DESIGN OF PARAMETER
ESTIMATION MODEL
A. PMSM Model
The mathematical model of the PMSM in dq-axis voltage
equation is given as
⎧
⎪
⎨
⎪
⎩
u
d
= Ri
d
+ L
d
di
d
dt
− L
q
ωi
q
u
q
= Ri
q
+ L
q
di
q
dt
+ L
d
ωi
d
+ ψ
m
ω
(1)
where ω is the electrical angular velocity, u
d
, u
q
, i
d
,andi
q
,
are dq-axis stator voltage and current. The elements of the
parameter set{R, L
d
, L
q
, ψ
m
} are the motor winding resis-
tance, magnet flux, d-axis and q-axis inductances, respectively,
which are usually unknown to the users. Note that the esti-
mated resistance R, as a lumped circuit resistance, includes
two parts, namely, the
ON-state slope resistances of the active
switch and freewheeling diode in inverter and terminal wire
resistance. At steady state the (1) can be discretized as follows:
u
d
(k) = Ri
d
(k) − L
q
ω(k)i
q
(k)
u
q
(k) = Ri
q
(k) + L
d
ω(k)i
d
(k) + ψω(k).
(2)
In a PMSM vector control system, the voltages used for the
PMSM parameter estimation are usually measured from the
output voltage of the current controllers, and the terminal
voltages of PMSM are PWM pulses from VSI which are dif-
ficult to measure directly [22]–[24]. The two output voltages,
denoted by u
∗
d
and u
∗
q
,areshowninFig.1.Notethatthere
exists an error between the reference voltage of the controller
and the actual output voltage of the VSI due to the nonlinearity
of VSI, so it is essential to estimate VSI nonlinearity.
Taking into account the influence of VSI nonlinearity,
the model of PMSM and VSI as a whole, for surface-mounted
PMSM, d-axis inductance is regarded as equal to q-axis
inductance, that is L
d
= L
q
= L, (2) can be rewritten as
u
∗
d
(k) + D
d
(k)V
dead
= Ri
d
(k) − Lω(k)i
q
(k) (3a)
u
∗
q
(k) + D
q
(k)V
dead
= Ri
q
(k) + Lω(k)i
d
(k) + ψ
m
ω(k)
(3b)
where D
d
and D
q
are the function of rotor position [13],
in (3) L, R, ψ
m
and V
dead
are the parameters to be estimated.
The variable V
dead
is the distorted voltage due to VSI
Fig. 2. Schematic of estimation and mathematical model.
nonlinearity, and can be represented as
V
dead
=
T
dead
+ T
ON
− T
OFF
T
s
· (V
dc
−V
sat
+ V
d
) +
V
sat
+ V
d
2
(4)
where T
dead
is the dead-time period of the switching device,
T
ON
and T
OFF
are turn-ON and turn-OFF times of the switching
device, V
dc
is measured real-time dc bus voltages, V
sat
and V
d
are the saturation voltage drop of the active switch and the
forward voltage drop of the freewheeling diode, T
s
is the
switching period. It can be seen that if variable V
dead
is
ignored, the estimation results may also be influenced by the
nonzero VSI nonlinearity terms (D
d
· V
dead
and D
q
· V
dead
),
and this may introduce an error into the estimation of the
PMSM parameters.
B. Design of Estimation Model Based
on Parameter Optimization
Apparently, the rank of (3) <3, while the number of
unknown parameters is four, thus the (3) is rank deficient,
the four parameters in (3) are not be identifiable and an
estimate to converge to suboptimal. To solve this problem,
a full rank reference model should be constructed if all these
parameters need to be estimated simultaneously at steady state.
Generally, d-axis current injection method is employed to
obtain more state equations due to the variation of d-axis
current. The parameters of machine can be assumed to be
constant as the duration of injected pulse current is very short
due to mechanical inertia and fast response of current loop PI
controller. In this case, the influence of injecting a short pulse
of i
d
on output torque and speed can be negligible. Thus,
the two sets of steady state data (Data0 and Data1) can be
used together for the estimation machine parameters and VSI
nonlinearity simultaneously modeling. An illustration is given
in Fig. 2, where i
d0
= 0 (A) during normal operation for the
decoupling the flux and torque control of SPMSM, and a very
short time of i
d1
= 0 (A) is injected to obtain another dq-axis
voltage equation model. Two groups of equations at i
d
= i
d0