Double Internal Model Control for Permanent Magnet Synchronous motor vector control system

Fig. 1. Block diagram of dynamic coupling of PMSM
ª «¬
I I
d q
(s)º (s)»¼
=
ª «¬
Rs + sLd ωLd
− Rs
ω Lq + sLq
º »¼
−1
ªU «¬U
d
' q
(s)º (s)»¼
(4)
III. IMC AND DECOUPLING
u
' q
transfer function matrix is described as (4).
978-1-4673-8721-7/16/$31.00 ©2016 IEEE
ud + +
1
id
Rs + Ld s
ωLq
uq + − − ωψ f
ωLd 1
Rs + Lq s iq
Equation (1) can be transformed to a transfer function
matrix after treating ωψf as a quasi-constant auxiliary input
signal
which
is
included
in
the
q
axis
voltage:
To improve the current control effect, researchers have proposed many control schemes, such as PI decoupling control [1-2], predictive control [3] and feed-forward decoupling [4-5]. The PI decoupling control is simple ,but the accuracy is not very high. The computation amount of the predictive control is large. The feed-forward decoupling highly depends on the motor parameters. IMC as an advanced control strategy is widely used in decoupling control [6-7]. Based on internal model decoupling and cross decoupling, a dynamic decoupling control scheme is proposed [6]. But the scheme is very complex. An IMDC is designed [7]. The current response rate is fast, but steady state error is large. In order to achieve good
+ ωψ
f
(1)

Te = 1.5np[ψ f iq + (Ld − Lq )idiq ]
(2)
Jdω / dt = Te − Bω − TL
(3)
Where ud and uq are the applied d-q axis voltages, id and iq are the d-q axis currents, Rs is the stator resistance, ω is the rotor speed, Ld and Lq are the d direction inductance and q direction inductance respectively, np is the number of pole pairs, J is the total moment of inertia, B is the viscous coefficient, ψf is the rotor flux. Te and TL are the electromagnetic torque and load torque respectively. Furthermore, for a surface mounted PMSM, which is commonly seen in practical applications, the d-q axis inductance satisfies Ld =Lq. Fig. 1 shows the structure of dynamic coupling of PMSM. The crosscoupling terms exist clearly, namely, ωLq and ωLd which vary quickly as speed and torque changes.
Keywords—permanent magnet synchronous motor; internal model control; two degree of freedom (2DOF); decoupling;
I. INTRODUCTION
PMSM has the advantages of simple structure, small size, high power factor, low rotational inertia. In fact it has been widely used in servo system, aerospace, numerical control machine, robot and some other areas. However, PMSM is a multivariable system with nonlinearity, strong coupling and time-varying characteristic. In order to achieve fine speedregulating performance, the excellent current control of the PMSM is important. Besides, the proportional integral (PI) controller can not regulate the speed tracking and load disturbance respectively.
Haowen Li, Zhao Meng, Gang Zheng, Haijing Wu
Faculty of Automation and Information Engineering Xi'an University of Technology Xi’an, China haowenli@
II. ELECTRICAL MODEL FOR PMSM
In this section, the PMSM is modeled in rotor coordinates (the d-q frame) .
­u ¯®u
d q
= =
Rsid Rsiq
+ Ld did / dt − ωLqiq + Lqdiq / dt + ωLdid
Abstract—Recently, the internal model control (IMC) theory is widely applied to the permanent magnet synchronous motor (PMSM) vector control system. In this paper, a double internal model control (DIMC) is proposed. The DIMC contains an improved internal model decoupling control (IMDC) and a simplified two degree of freedom internal model control (2DOFIMC). First, in current loop, the improved IMDC can address the issue that there is a trade-off between decoupling effect, response speed and steady state error during the selection of the sole adjustable parameter in the conventional IMDC. Second, in speed loop, the simplified 2DOF-IMC can make the performances on speed tracking and disturbance rejection be regulated independently, and can simplify the structure of the speed controller. According to the simulation results, the DIMC for PMSM vector control system shows good performances on current decoupling and high current control accuracy. The speed-regulating performance is promising.
2016 IEEE Canadian Conference on Electrical and Computer Engineering (CCECE)
Double Internal Model Control for Permanent Magnet Synchronous Motor Vector Control System