Hindawi Publishing Corporation Mathematical Problems in Engineering Volume 2016, Article ID 3690240, 14 pages http://dx.doi.org/10.1155/2016/3690240
Research Article Adaptive Robust Backstepping Control of Permanent Magnet Synchronous Motor Chaotic System with Fully Unknown Parameters and External Disturbances Yang Yu, Xudong Guo, and Zengqiang Mi State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Baoding 071003, China Correspondence should be addressed to Yang Yu; ncepu
[email protected] Received 15 December 2015; Revised 16 March 2016; Accepted 30 March 2016 Academic Editor: Shengjun Wen Copyright Β© 2016 Yang Yu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The chaotic behavior of permanent magnet synchronous motor is directly related to the parameters of chaotic system. The parameters of permanent magnet synchronous motor chaotic system are frequently unknown. Hence, chaotic control of permanent magnet synchronous motor with unknown parameters is of great significance. In order to make the subject more general and feasible, an adaptive robust backstepping control algorithm is proposed to address the issues of fully unknown parameters estimation and external disturbances inhibition on the basis of associating backstepping control with adaptive control. Firstly, the mathematical model of permanent magnet synchronous motor chaotic system with fully unknown parameters is constructed, and the external disturbances are introduced into the model. Secondly, an adaptive robust backstepping control technology is employed to design controller. In contrast with traditional backstepping control, the proposed controller is more concise in structure and avoids many restricted problems. The stability of the control approach is proved by Lyapunov stability theory. Finally, the effectiveness and correctness of the presented algorithm are verified through multiple simulation experiments, and the results show that the proposed scheme enables making permanent magnet synchronous motor operate away from chaotic state rapidly and ensures the tracking errors to converge to a small neighborhood within the origin rapidly under the full parameters uncertainties and external disturbances.
1. Introduction In recent years, the permanent magnet synchronous motor (PMSM) is utilized widely in various industrial fields due to its constantly dropping production cost, simple structure, high torque, and high efficiency. However, Hemati found that PMSM would generate chaotic behavior with system parameters entering into a certain region [1]. Previous studies have shown that the chaotic movement of PMSM will produce irregular oscillations of torque and speed, exacerbate current noise, and worsen operation performance and may even damage the entire drive system. Therefore, research on PMSM chaos phenomenon has attracted extensive attention worldwide [2β5], and further studying on the control method of PMSM chaos is of extreme significance [6β8]. The nonlinear characteristics of PMSM, such as multivariability, strong coupling, and high dimension, make it difficult to control for traditional linear control theory. Hence,
a variety of modern and nonlinear control algorithms are introduced to suppress PMSM chaotic behavior. In terms of these control algorithms whether or not relying on the model parameters, the previous control methods can primarily be divided into two categories. The first type is on the basis of accurate model parameters, such as entrainment and migration control [9], exact feedback linearization control [10], and decoupling control [11]. However, the accuracy of these control methods directly depends on PMSM model parameters; if the system parameters deviate from the rated values, the control performance will go bad. The second type is based on unknown parameters, which have become the research focus of PMSM chaos suppression recently, mainly including sliding mode variable structure control [12, 13], fuzzy control [14], and π»β control [15]. However, sliding mode variable structure control requires uncertain parameters to satisfy certain matching conditions, fuzzy control is
2 dependent on the fuzzification of Takagi-Sugeno, and π»β control is inclined to ignore the operating states under special conditions [16]. In essence, PMSM chaotic system is highly sensitive to initial states and parameters, and PMSM model parameters are susceptible to the temperature and humidity of the surrounding environment. Therefore, PMSM chaotic repression with unknown model parameters has applicability to a broader field and is more in line with reality [17]. Actually, the adaptive control (AC) provides a natural routine for PMSM chaotic control with unknown parameters, which has been presented in literatures [12, 13, 18]. Backstepping control (BC) is one of the most popular nonlinear control methods newly proposed to address parameter uncertainty, specifically the uncertainty not satisfying matching condition, which has been successfully applied to many engineering fields such as motor drive, temperature control of boiler main steam, and rocket location tracking. The core idea of BC is that complex highdimensional nonlinear systems are decomposed into many simple low-dimensional subsystems and virtual control variables are introduced to backstepping process to design concrete controllers. In addition, BC has been successfully applied to suppress Liu chaotic system [19] and Chen chaotic system [20]. Therefore, the idea of combining BC with AC provides a useful and feasible train of thought to control PMSM chaotic system with unknown parameters. Literatures [21, 22] have exactly practiced this idea. However, the conventional backstepping approach is confronted with two major problems of solving complicated βregression matrixβ [23] and encountering βexplosion of termsβ [24]. In [25], the complexity of regression matrix is sufficiently manifested, which almost occupies one full page. Nevertheless, explosion of terms is an inherent shortcoming and is induced by repeated differentiations of virtual variables, particularly in design of adaptive backstepping controller [26]. Additionally, integration of BC with AC is frequently faced with the singularity arising from any estimation term emerging as a denominator of any control input. The overparameterization caused by the number of estimations larger than actual system parameters hinders the conventional adaptive backstepping control. In addition to the above problems, to the extent of our knowledge, mostly existing literatures on PMSM chaotic control only concentrate on the cases of single unknown parameter and partial unknown parameters [21, 22], and there is no way to address the issue of fully unknown parameters. Furthermore, the existing researches mainly aim at the situation of sudden power failure during PMSM operation [16]; the existing conclusions lack the generality. Hence, through combination of BC and AC, not only does this paper study the control issue of PMSM chaos suppression with fully unknown parameters, but also the external disturbances are taken into account in PMSM chaos model. Newly adaptive updating laws of unknown parameters are designed to totally estimate unknown parameters of PMSM chaotic model, and adaptive robust backstepping controllers on the basis of adaptive estimations and external disturbances are developed to drive PMSM to escape out of chaotic state quickly, inhibit the external disturbances, and accomplish the given signals
Mathematical Problems in Engineering tracking rapidly. The method proposed in this paper expands the applied range of backstepping control theory in PMSM chaotic system. Moreover, the study of chaos control problem with totally unknown parameters and external disturbances is more general and practical, and the results and conclusions obtained are more applicable.
2. PMSM Chaotic Model with Fully Unknown Parameters For a PMSM, its mathematical model in ππ axis coordinate system can be described as follows [16]: 3πππ Μ π΅ πΜ Μ β π, ΜΜ = ππ β π π 2π½ π½ π½ ππ 1 ΜππΜ = β π
Μππ β ππ Μ β
Μππ β π β
π Μ + π’Μπ , πΏπ πΏπ πΏπ
(1)
1 ΜππΜ = β π
Μππ + ππ Μ β
Μππ + π’Μ , πΏπ πΏπ π Μ is the mechanical angular velocity of the rotating where π rotor, Μππ and Μππ are π axis and π axis currents of stator winding, respectively, π’Μπ and π’Μπ are π axis and π axis voltages of stator winding, π is the number of rotor pole pairs, ππ is the flux generated by permanent magnets, π½ is the moment of inertia, π΅ is the viscous damping coefficient, πΜπ is the load torque, π
is the phase resistance of the stator windings, and πΏ π and πΏ π are π axis and π axis inductances of stator winding, respectively. For a PMSM with uniform air gap, πΏ π = πΏ π . Hence, we use πΏ to substitute πΏ π and πΏ π in the following paper. Μ π
Selecting [
π 1/ππ 0 0 π 0 π 0][ π ] ππ 0 0 π
the
affine
transformation
[ Μππ ] Μππ
=
and time scale transformation Μπ‘ = ππ‘, the
PMSM mathematical model described in (1) can be converted into dimensionless form as follows: 1 πΜ = (ππ β π) β ππ , πΏ (2) π Μ = βπ β π β
π + πΎ β
π + π’ , π
π
π
π
ππΜ = βππ + π β
ππ + π’π , where π = πΏ/π
, π = 2π΅/3π2 πππ , π’π = (1/ππ
)Μ π’π , πΎ = βππ /ππΏ, 2 Μ π’π = (1/ππ
)Μ π’π , πΏ = π½/π΅π, and ππ = ππ ππ /π½. As presented in (2), the dynamic performance of PMSM depends on three parameters πΏ, πΎ, and ππ . Considering the most general case, let πΏ = 0.2, πΎ = 50, ππ = 3.2, π’π = β0.6, and π’π = 0.8. If the initial state is selected as (π, ππ , ππ ) = (0, 0, 0), PMSM system will run on a chaotic state and display the chaotic behavior. A typical chaotic attractor of PMSM is manifested in Figure 1. In reality, the three parameters πΏ, πΎ, and ππ in (2) tend to be unknown or to have uncertainties resulting from operating conditions. In other words, when all the parameters πΏ, πΎ, and ππ cannot be determined, (2) actually represents PMSM chaotic system model with fully unknown parameters.
id
Mathematical Problems in Engineering 90 80 70 60 50 40 30 20 10 0 β10 30
3 The estimated values of unknown system parameters are Μ πΎΜ, and Μ πΎΜ, and πΜ ; then, the estimation errors πΏ, described as πΏ, π πΜπ can be expressed as follows: πΏΜ = πΏΜ β πΏ, πΎΜ = πΎΜ β πΎ,
20
(4)
πΜπ = πΜπ β ππ . 10 0 β10 β20 iq β30 β40 β50
β20
0 β10 β5 π β15
5
10
15
Figure 1: Chaotic attractor of PMSM system.
3. Design of Adaptive Robust Controller with Backstepping Approach Taking a more general situation into account, the PMSM chaotic model described in (2) is immersed by external disturbances. The model can be rewritten as follows: 1 πΜ = (ππ β π) β ππ , πΏ ππΜ = βππ β π β
ππ + πΎ β
π + π’π + Ξ 1 (x, π‘) ,
3.2. Controller Design. The essence of adaptive robust backstepping controller is to design controller through combination of backstepping method and adaptive approach; then, a reasonably stable function is built in accordance with Lyapunov stability theory to guarantee error variables to be effectively stabilized and meanwhile ensure the output of closed loop system tracks reference signals quickly. On the basis of this, the adaptive robust backstepping controller is designed as follows. Step 1. For the speed reference signal πβ , define the tracking error ππ as follows: ππ = π β πβ .
(5)
Taking PMSM chaotic system model (3) into account, the derivative of (5) can be written as (3)
ππΜ = βππ + π β
ππ + π’π + Ξ 2 (x, π‘) , where Ξ 1 (x, π‘) and Ξ 2 (x, π‘) represent the external disturbances, x indicates the system states, and x = (π₯1 , π₯2 , π₯3 ) = (π, ππ , ππ ). 3.1. Control Objective and Assumptions. Control problem in the paper can be described as follows: for PMSM chaotic system (3) with fully unknown parameters πΏ, πΎ, and ππ and external disturbances Ξ 1 and Ξ 2 , adaptive laws of unknown parameters πΏ, πΎ, and ππ are designed and adaptive robust controllers π’π and π’π are constructed to ensure PMSM breaks away from chaos rapidly and runs into an expected orbit. Simultaneously, the fully unknown parameters πΏ, πΎ, and ππ can be estimated accurately and the external disturbances can be inhibited effectively. For convenience of controller design, the control system is supposed to hold some reasonable assumptions as follows. Assumption 1. The state variables for PMSM chaotic system (π, ππ , ππ ) are observable. Assumption 2. The external disturbances Ξ π (x, π‘) satisfy the condition |Ξ π (x, π‘)| β€ ππ (x)ππ (π‘), π = 1, 2, where ππ (x) is a known function, ππ (π‘) is an unknown but bounded timevarying function, and |ππ (π‘)| β€ ππmax , where ππmax is a constant. Assumption 3. The desired speed and π axis current reference signals πβ and ππβ and their derivatives are known and bounded.
1 (6) (π β π) β ππ β πΜ β . πΏ π Define the tracking error ππ of π axis stator current ππ as follows: ππΜ = πΜ β πΜ β =
ππ = ππ β ππβ ,
(7)
ππβ
where is the expected output value of ππ . For the π axis current reference signal ππβ , its tracking error ππ is defined as follows: ππ = ππ β ππβ .
(8)
By substitution of (7) into (6), we can obtain ππΜ =
1 (π + πβ β π) β ππ β πΜ β πΏ π π
1 = (ππβ β π) β πΜπ + πΜπ β πΜ β . πΏ
(9)
Let ππβ = π + πΏΜ (Μππ + πΜ β β π1 ππ ) ,
(10)
ππβ = 0,
(11)
where π1 represents the positive control gain. Through substitution of (10) into (9), (12) can be obtained: ππΜ =
πΏΜ 1 ππ + (Μππ + πΜ β β π1 ππ ) β πΜπ + πΜπ β πΜ β πΏ πΏ
=
1 πΏ + πΏΜ ππ + (Μππ + πΜ β β π1 ππ ) β πΜπ + πΜπ β πΜ β πΏ πΏ
=
πΏΜ 1 ππ + (Μππ + πΜ β β π1 ππ ) + πΜπ β π1 ππ . πΏ πΏ
(12)
4
Mathematical Problems in Engineering
Lyapunov function π1 is selected as follows: 1 π1 = ππ2 . 2 Then, the derivative of π1 can be described as
β πΏΜ (πΜΜπ + πΜ β ) + (13)
β
π1 β
πΜ β = βππ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π + Ξ 1
πΜ 1 = ππ ππΜ πΏΜ 1 = ππ ( ππ + (Μππ + πΜ β β π1 ππ ) + πΜπ β π1 ππ ) . πΏ πΏ
1 Μ β πΏΜ (Μππ + πΜ β β π1 β
ππ ) β ππ πΏ
(14)
β
Step 2. To stabilize the output π axis current of PMSM, the derivative of ππ is conducted as follows:
πΏΜ (Μπ + πΜ β β π1 β
ππ ) β πΜπ + π1 β
ππ β πΜ β πΏ π
πΏΜ β πΏΜ (πΜΜπ + πΜ β ) + β
π1 β
(ππ β π) β πΏΜ β
π1 πΏ
β ππΜ = ππΜ β ππΜ = βππ β π β
ππ + πΎ β
π + π’π + Ξ 1 β [πΜ
β
(Μππ β πΜπ ) β πΏΜ β
π1 β
πΜ β
Μ + πΏΜ (Μππ + πΜ β β π1 β
ππ ) + πΏΜ (πΜΜπ + πΜ β β π1 β
ππΜ )]
= βππ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π + Ξ 1
= βππ β π β
ππ + πΎ β
π + π’π + Ξ 1 β [πΜ Μ + πΏΜ (Μππ + πΜ β β π1 β
ππ ) + πΏΜ (πΜΜπ + πΜ β β π1 β
ππΜ )]
πΏΜ β
π β
(π β π) β πΏΜ β
π1 β
ππ β πΏΜ πΏ 1 π
1 Μ β πΏΜ (Μππ + πΜ β β π1 β
ππ ) β ππ πΏ (15)
πΏΜ (Μπ + πΜ β β π1 β
ππ ) β πΜπ + π1 β
ππ β πΜ β πΏ π
Μ = βππ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π + Ξ 1 β πΏΜ (Μππ
β
+ πΜ β β π1 β
ππ ) β πΜ β πΏΜ (πΜΜπ + πΜ β β π1 β
ππΜ ) = βππ
πΏΜ β πΏΜ (πΜΜπ + πΜ β ) + β
π1 β
(ππ β π) β πΏΜ β
π1 β
πΜπ + πΏΜ πΏ
Μ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π + Ξ 1 β πΏΜ (Μππ + πΜ β β π1
β
π1 β
πΜπ β πΏΜ β
π1 β
πΜ β . (17)
β
ππ ) β ππΜ β πΜ β β πΏΜ (πΜΜπ + πΜ β ) + πΏΜ β
π1 (π β πΜ β ) .
By substitution of πΏΜ = πΏΜ + πΏ into (17), the following equation can be obtained:
By substitution of (12) into (15), we can get ππΜ = βππ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π + Ξ 1 1 Μ β πΏΜ (Μππ + πΜ β β π1 β
ππ ) β ππ πΏ πΏΜ β (Μππ + πΜ β β π1 β
ππ ) β πΜπ + π1 β
ππ β πΜ β πΏ
ππΜ = βππ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π + Ξ 1 (16)
β πΏΜ (πΜΜπ + πΜ β ) + πΏΜ β
π1 (π β πΜ β ) . Combined with the mathematical model of PMSM chaotic system, (16) can be further calculated as follows: ππΜ = βππ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π + Ξ 1 1 Μ β πΏΜ (Μππ + πΜ β β π1 β
ππ ) β ππ πΏ β
πΏΜ (Μπ + πΜ β β π1 β
ππ ) β πΜπ + ππ β
ππ β πΜ β πΏ π
β πΏΜ (πΜΜπ + πΜ β ) + πΏΜ β
π1 β
ππ β π β ππ πΏ
β πΏΜ β
π1 β
πΜ β
= βππ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π + Ξ 1 1 Μ β πΏΜ (Μππ + πΜ β β π1 β
ππ ) β ππ πΏ β
πΏΜ (Μπ + πΜ β β π1 β
ππ ) β πΜπ + π1 β
ππ β πΜ β πΏ π
1 Μ β πΏΜ (Μππ + πΜ β β π1 ππ ) β ππ πΏ β
πΏΜ (Μπ + πΜ β β π1 ππ ) β πΜπ + π1 ππ β πΜ β πΏ π
β πΏΜ (πΜΜπ + πΜ β ) +
πΏ + πΏΜ β
π1 β
(ππ β π) β πΏΜ β
π1 β
πΜπ πΏ
+ πΏΜ β
π1 β
πΜπ β πΏΜ β
π1 β
πΜ β = βππ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π + Ξ 1
(18)
1 Μ β πΏΜ (Μππ + πΜ β β π1 ππ ) β ππ πΏ β
πΏΜ (Μπ + πΜ β β π1 ππ ) β πΜπ + π1 ππ β πΜ β πΏ π
πΏΜ β πΏΜ (πΜΜπ + πΜ β ) + π1 β
(ππ β π) + β
π1 β
(ππ β π) πΏ β πΏΜ β
π1 β
πΜπ + πΏΜ β
π1 β
πΜπ β πΏΜ β
π1 β
πΜ β . Lyapunov function π2 is chosen as follows: 1 π2 = π1 + ππ2 . 2
(19)
Mathematical Problems in Engineering
5
Then, the derivative of π2 can be described as
β
πΏΜ 1 πΜ 2 = πΜ 1 + ππ ππΜ = ππ ( ππ + (Μππ + πΜ β β π1 ππ ) + πΜπ πΏ πΏ
πΏΜ ((Μππ + πΜ β β π1 ππ ) β π1 β
(ππ β π)) πΏ
+ πΜπ (πΏΜ β
π1 β 1)) . (24)
β π1 ππ ) + ππ (βππ β π β
ππ + πΎΜ β
π β πΎΜ β
π + π’π 1 Μ + Ξ 1 β πΏΜ (Μππ + πΜ β β π1 ππ ) β ππ πΏ β
πΏΜ (Μπ + πΜ β β π1 ππ ) β πΜπ + π1 ππ β πΜ β πΏ π
β πΏΜ (πΜΜπ + πΜ β ) + π1 β
(ππ β π) +
Additionally, (20)
ππ (β
β€β
πΏΜ β
π β
(π β π) πΏ 1 π
π’ππ = βπ2 β
ππ + ππ + π β
ππ β πΎΜ β
π
1 π3 = π2 + ππ2 . 2
(22)
πΜ 3 = πΜ 2 + ππ ππΜ β
= πΜ 2 + ππ (βππ + π β
ππ + π’π + Ξ 2 β ππΜ ) .
where π2 is another positive control gain and π1 is a positive number chosen arbitrarily. By substitution of (21) and (22) into (20), we can acquire
β π1 ππ ) + ππ (βπ2 ππ β
1 β
π + π1 ππ β πΎΜ β
π + π’ππ πΏ π
πΏΜ + Ξ 1 β ((Μππ + πΜ β β π1 ππ ) β π1 β
(ππ β π)) πΏ 1 + πΜπ (πΏΜ β
π1 β 1)) = ππ ( ππ πΏ πΏΜ + (Μππ + πΜ β β π1 ππ ) + πΜπ β π1 ππ ) + ππ (βπ2 ππ πΏ β
π2 (x) 1 π + Ξ1 β
ππ + π1 ππ β πΎΜ β
π β 1 πΏ 4π1 π
(27)
Then, the derivative of π3 can be represented as
(23)
πΏΜ 1 πΜ 2 = πΜ 1 + ππ ππΜ = ππ ( ππ + (Μππ + πΜ β β π1 ππ ) + πΜπ πΏ πΏ
(26)
Lyapunov function π3 is chosen as
β
π1 β
πΜπ + πΏΜ β
ππ β
πΜ β β π1 (ππ β π) , π12 (x) π, 4π1 π
2βπ1
2 2 β βπ1 π1max ) + π1 π1max .
β β ππΜ = ππΜ β ππΜ = βππ + π β
ππ + π’π + Ξ 2 β ππΜ .
(21)
where π’ππ and π’ππ are the model compensation and robust control inputs, respectively. Then, π’ππ and π’ππ can be, respectively, chosen as
π’ππ = β
σ΅¨ σ΅¨ π1 (x) σ΅¨σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨σ΅¨
(25)
Step 3. Differentiating the tracking error ππ of π axis current ππ , we can get
The first control variable is selected as
Μ + πΏΜ (Μππ + πΜ β β π1 ππ ) + πΜ β + πΏΜ (πΜΜπ + πΜ β ) + πΏΜ
π12 (x) 2 σ΅¨ σ΅¨ ππ + π1 (x) π1max σ΅¨σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨σ΅¨ 4π1
= β(
β πΏΜ β
π1 β
πΜπ + πΏΜ β
π1 β
πΜπ β πΏΜ β
π1 β
πΜ β ) .
π’π = π’ππ + π’ππ ,
π12 (x) π2 (x) 2 ππ + Ξ 1 ) = β 1 π + Ξ 1 ππ 4π1 4π1 π
(28)
In terms of (28), π axis output stator voltage π’π can be calculated: π’π = π’ππ + π’ππ ,
(29)
π’ππ = βπ3 β
ππ + ππ β π β
ππ + ππβ ,
(30)
where
π’ππ = β
π22 (x) π , 4π2 π
(31)
where π3 is the positive control gain and π2 is a positive number chosen arbitrarily. By substitution of (30) and (31) into (26) and (28), respectively, the following equations can be acquired: ππΜ = βπ3 β
ππ + π’ππ + Ξ 2 = βπ3 β
ππ β
π22 (x) π + Ξ 2, 4π2 π
(32)
πΜ 3 = πΜ 2 + ππ ππΜ = πΜ 2 + ππ (βπ3 β
ππ β
π22 (x) π + Ξ 2) , 4π2 π
(33)
6
Mathematical Problems in Engineering ππ (β
π22 (x) π2 (x) 2 ππ + Ξ 2 ) = β 2 π + Ξ 2 ππ 4π2 4π2 π
β€β
+
π22 (x) 2 σ΅¨ σ΅¨ π + π2 (x) π2max σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨ 4π2 π
= β(
(34)
2 σ΅¨ σ΅¨ π2 (x) σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨ 2 β βπ2 π2max ) + π2 π2max . 2βπ2
Step 4. Lyapunov function π of PMSM chaotic system with fully unknown parameters and external disturbances is selected as follows: π = π3 +
1 2 1 2 1 Μ2 πΏ, πΜ + πΎΜ + 2π1 π 2π2 2πΏ β
π3
(35)
where π1 , π2 , and π3 represent positive adaptive gains. Μ ΜΜ πΎΜΜ = πΎΜΜ , and πΜΜ = πΜΜ , Combined with equations πΏΜ = πΏ, π π derivative of selected Lyapunov function π can be calculated as follows: πΎΜ πΜ πΏΜ ΜΜ πΏ = πΜ 2 + ππ (βπ3 β
ππ πΜ = πΜ 3 + π πΜΜπ + πΎΜΜ + π1 π2 πΏ β
π3 1 + π’ππ + Ξ 2 ) = πΜ 1 + ππ (βπ2 ππ β β
ππ + π1 ππ β πΎΜ πΏ β
π + π’ππ + Ξ 1 πΏΜ β ((Μππ + πΜ β β π1 ππ ) β π1 β
(ππ β π)) πΏ
1 πΏΜ = ππ ( ππ + (Μππ + πΜ β β π1 ππ ) + πΜπ β π1 ππ ) πΏ πΏ
πΏΜ ((Μππ + πΜ β β π1 ππ ) β π1 β
(ππ β π)) πΏ
β
ππ ππ +
πΏΜ (Μπ + πΜ β β π1 ππ ) β
ππ + πΜπ ππ β π1 ππ2 πΏ π
1 β π3 ππ2 β π2 ππ2 β πΎΜπππ β ππ2 + ππ (π’ππ + Ξ 1 ) πΏ + ππ (π’ππ + Ξ 2 ) β
πΏΜ ((Μππ + πΜ β β π1 ππ ) πΏ
β π1 (ππ β π)) β
ππ + πΜπ (πΏΜ β
π1 β 1) ππ + π1 ππ ππ +
πΎΜ πΜπ Μ πΏΜ ΜΜ 1 πΏ = ππ ππ + π1 ππ ππ πΜπ + πΎΜΜ + π1 π2 πΏπ3 πΏ
Μ πΏΜ ] β π1 ππ2 β π2 ππ2 β π3 ππ2 π3
Μ Μ Μ π + πΜπ ] + πΎΜ [βππ + πΎΜ ] + πΜπ [ππ β ππ + πΏπ 1 π π π1 π2 2
2
π (x) π (x) 1 π + Ξ 1 ) + ππ (β 2 π β ππ2 + ππ (β 1 πΏ 4π1 π 4π2 π + Ξ 2) . (36) In terms of (36), the adaptive laws of unknown parameters πΏ, πΎ, and ππ can be selected, respectively, as follows: Μ πΏΜ = βπ3 [(Μππ + πΜ β β π1 ππ ) β
(ππ β ππ )
(37)
+ π1 (ππ β π) ππ ] , πΎΜΜ = π2 πππ ,
(38)
Μ π ]. πΜΜπ = βπ1 [ππ β ππ + πΏπ 1 π
(39)
1 1 πΜ = ππ ππ + π1 ππ ππ β π1 ππ2 β π3 ππ2 β π2 ππ2 β ππ2 πΏ πΏ
1 + ππ (βπ2 ππ β β
ππ + π1 ππ β πΎΜ β
π + π’ππ + Ξ 1 πΏ
+ πΜπ (πΏΜ β
π1 β 1)) + ππ (βπ3 β
ππ + π’ππ + Ξ 2 ) =
+ π1 (ππ β π) ππ +
By substitution of (37), (38), and (39) into (36), (36) can be simplified as follows:
+ πΜπ (πΏΜ β
π1 β 1)) + ππ (βπ3 β
ππ + π’ππ + Ξ 2 )
β
πΏΜ [(Μππ + πΜ β β π1 ππ ) ππ β (Μππ + πΜ β β π1 ππ ) ππ πΏ
1 πΏ
+ ππ (β
π12 (x) π + Ξ 1) 4π1 π
+ ππ (β
π22 (x) π + Ξ 2) . 4π2 π
(40)
3.3. Stability Analysis Theorem 4. For PMSM chaotic system model (3) with fully unknown parameters and external disturbances, design of adaptive control laws (37), (38), and (40) and selection of suitable controller gains π1 , π2 , π3 , π1 , and π2 and adaptive gains π1 , π2 , and π3 , the proposed adaptive robust backstepping controllers (21) and (29) can ensure the tracking error signals (5), (7), and (8) of PMSM chaotic systems are asymptotically stable. That is to say, PMSM chaotic system can run out of chaos quickly through the proposed controllers (21) and (29) and track the given reference signals. Through stability analysis, we want to verify the correctness of the theorem.
Mathematical Problems in Engineering
7
According to (40), new expression can be obtained as follows through some mathematical computations: 1 1 πΜ = ππ ππ + π1 ππ ππ β π1 ππ2 β π3 ππ2 β π2 ππ2 β ππ2 πΏ πΏ + ππ (β =β
β(
2 2 π 1 1 1 (π β π ) + ππ2 + ππ2 β 1 (ππ β ππ ) 2πΏ π π 2πΏ 2πΏ 2
+
π12 (x) π2 (x) ππ + Ξ 1 ) + ππ (β 2 π + Ξ 2 ) (41) 4π1 4π2 π
2 2 π 1 (π β π ) β 1 (ππ β ππ ) β π3 ππ2 2πΏ π π 2
+(
π12 (x) π + Ξ 1) 4π1 π
+ ππ (β
π22 (x) π + Ξ 2) . 4π2 π
2 2 π 1 (π β π ) β 1 (ππ β ππ ) β π3 ππ2 β π4 ππ2 2πΏ π π 2 2 σ΅¨ σ΅¨ π1 (x) σ΅¨σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨σ΅¨ β π5 ππ2 β ( β βπ1 π1max ) 2βπ1
β(
2 σ΅¨ σ΅¨ π2 (x) σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨ β βπ2 π2max ) + π0 , 2βπ2
(44)
π π 1 1 1 + 1 β π1 ) ππ2 + ( + 1 β π2 β ) ππ2 2πΏ 2 2πΏ 2 πΏ
+ ππ (β
2 σ΅¨ σ΅¨ π2 (x) σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨ 2 β βπ2 π2max ) + π2 π2max 2βπ2
β€β
π1 2 π1 2 1 π + π β π1 ππ2 β π3 ππ2 β π2 ππ2 β ππ2 2 π 2 π πΏ
+ ππ (β =β
π12 (x) π2 (x) ππ + Ξ 1 ) + ππ (β 2 π + Ξ 2) 4π1 4π2 π
2 2 π 1 (π β π ) β 1 (ππ β ππ ) β π3 ππ2 β π4 ππ2 2πΏ π π 2 2 σ΅¨ σ΅¨ π1 (x) σ΅¨σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨σ΅¨ 2 2 β π5 ππ β ( β βπ1 π1max ) + π1 π1max 2βπ1
β€β
where π4 = β(1/2πΏ + π1 /2 β π1 ) β₯ 0, π5 = β(1/2πΏ + π1 /2 β 2 2 + π2 π2max . π2 β 1/πΏ) β₯ 0, and π0 = π1 π1max Let π (π (π‘)) = β
β π4 ππ2 β π5 ππ2 β(
Appropriate controller gains π1 and π2 are selected as follows: (
π 1 + 1 β π1 ) < 0, 2πΏ 2
π 1 1 ( + 1 β π2 β ) < 0. 2πΏ 2 πΏ
β( (42)
1 , πΏ
1 π1 β 2π2 < . πΏ Then, by substitution of (43) into (41), we can obtain 2 2 π 1 πΜ = β (ππ β ππ ) β 1 (ππ β ππ ) β π3 ππ2 2πΏ 2
+(
π π 1 1 1 + 1 β π1 ) ππ2 + ( + 1 β π2 β ) ππ2 2πΏ 2 2πΏ 2 πΏ
π2 (x) + ππ (β 1 π + Ξ 1) 4π1 π + ππ (β
π22 (x) π + Ξ 2) 4π2 π
σ΅¨ σ΅¨ π1 (x) σ΅¨σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨σ΅¨ 2βπ1
2
β βπ1 π1max )
(45)
2 σ΅¨ σ΅¨ π2 (x) σ΅¨σ΅¨σ΅¨ππ σ΅¨σ΅¨σ΅¨ β βπ2 π2max ) + π0 , 2βπ2
where π(π‘) = (ππ , ππ , ππ ). By integration of (45), we can get π‘
π‘
π‘0
π‘0
β« π (π (π‘)) ππ‘ = β β« πΜ (π (π‘)) ππ‘ σ³¨β
Equation (42) can be replaced by the following: π1 >
2 2 π 1 (ππ β ππ ) β 1 (ππ β ππ ) β π3 ππ2 2πΏ 2
π‘
(43)
(46)
β« π (π (π‘)) ππ‘ = π (π‘0 ) β π (π‘) . π‘0
Since π(π‘0 ) is bounded and π(π‘) is bounded and nonincreasing, hence π‘
lim β« π (π (π‘)) ππ‘ < β.
π‘ββ π‘ 0
(47)
Μ Moreover, π(π(π‘)) is uniform continuous and π(π(π‘)) is bounded. In accordance with Barbalatβs Lemma, the following equation can be obtained: lim π (π (π‘)) = 0.
π‘ββ
(48)
Apparently, through selection of suitable controller gains π1 , π2 , π3 , π1 , and π2 , πΜ can be ensured to be negative definite. The above derivation has proved that the selected suitable controller gains π1 , π2 , π3 , π1 , and π2 and adaptive gains π1 , π2 ,
8 20
40
15
30
10
20
5
10
0
0 iq
π
Mathematical Problems in Engineering
β5
β10
β10
β20
β15
β30
β20
β40
β25
0
10
20
30
40
50 t (s)
60
70
80
90
β50
100
Figure 2: The π curve of PMSM chaotic system with no control inputs π’π and π’π .
20
30
40
50 t (s)
60
70
80
90
100
100 90 80 70
id
60
4. Numerical Simulation and Discussions
4.1. Test-I. The PMSM chaotic system is tested with the parameters πΏ = 0.2, πΎ = 50, and ππ = 3.2. In order to be consistent with the reality better, we assume that the three parameters of PMSM chaotic system are all unknown with the initial condition of (πΏ, πΎ, ππ ) = (0, 0, 0), and the expected reference signals are set as πβ = 10 and ππβ = 1. Furthermore, the external disturbances Ξ 1 (x, π‘) = 20π₯3 sin(5π‘) and Ξ 2 (x, π‘) = 10 sin(5π‘) are injected into the PMSM chaotic system. The simulation results given in Figures 2β4 apparently show PMSM runs in a chaotic state with no control inputs. Therefore, introduction of the presented control approach to suppress chaos in PMSM system will be of great importance and necessity. Figures 5β12 show that the proposed controller is utilized to control the PMSM chaotic system, where Figures 5β7 display the curves of state variables changing over time for PMSM chaotic system, which demonstrate the PMSM system stays away from the previous chaotic state when the designed controller is added to PMSM chaotic system, and track the desired signals accurately and rapidly. Furthermore,
10
Figure 3: The ππ curve of PMSM chaotic system with no control inputs π’π and π’π .
and π3 can make the inequalities of π β₯ 0 and πΜ < 0 hold. In addition, equation of π = 0 is not satisfied until ππ = ππ = ππ = πΜπ = πΎΜ = πΏΜ = 0. In summary, PMSM chaotic system is globally asymptotically stable at the equilibrium point of (ππ , ππ , ππ ) = (0, 0, 0).
In order to illustrate the superiority of the proposed approach adequately, the simulation is carried out in MATLAB environment for three cases under the initial condition of (π, ππ , ππ ) = (0, 0, 0). Let (π, ππ , ππ ) = (π₯1 , π₯2 , π₯3 ) and the control parameters are selected as π1 = 10, π2 = 30000, π3 = 5, and π1 = π2 = 0.01; the adaptive gains are chosen as π1 = 6.2, π2 = 100, and π3 = 0.06. The simulation time is chosen as 100 s and the designed controller is put into effect at the time of 20 s.
0
50 40 30 20 10 0
0
10
20
30
40
50 t (s)
60
70
80
90
100
Figure 4: The ππ curve of PMSM chaotic system with no control inputs π’π and π’π . 15 10 5 0 π
β5 β10 β15 β20 β25
0
10
20
30
40
50 t (s)
60
70
80
90
100
Figure 5: The π curve of PMSM chaotic system added the controller inputs π’π and π’π .
Mathematical Problems in Engineering
9
40
Γ104 9.66
30
9.64
20
9.62
10
9.6
iq
0 uq
β10
Γ104 9.62 9.61 9.6 9.59 9.58 9.57
9.56
β20
9.54
β30
9.52
β40 β50
9.58
60 60.05 60.1
9.5 0
10
20
30
40
50 t (s)
60
70
80
90
100
20
30
Figure 6: The ππ curve of PMSM chaotic system added the controller inputs π’π and π’π .
40
50
60 t (s)
70
80
90
100
90
100
Figure 9: The controller input π’π .
100 0.05
90 80
0 Estimation error of πΏ
70
id
60 50 40 30 20
β0.1
β0.15
10 0
β0.05
0
10
20
30
40
50 t (s)
60
70
80
90
100
β0.2 20
Figure 7: The ππ curve of PMSM chaotic system added the controller inputs π’π and π’π .
10
β2.68
0 Estimation error of πΎ
ud
Γ106 β2.7282
β2.7 β2.7288 60
β2.71
61
62
63
40
50
60 t (s)
70
80
Figure 10: The πΏΜ curve of estimation error of πΏ.
Γ106 β2.67
β2.69
30
β10 β20 β30
β2.72 β40
β2.73 20
30
40
50
60 t (s)
70
80
Figure 8: The controller input π’π .
90
100
β50 20
30
40
50
60 t (s)
70
80
90
Figure 11: The πΎΜ curve of estimation error of πΎ.
100
Mathematical Problems in Engineering 0.5
40
0
30
β0.5
20
β1
10
β1.5
iq
Estimation error of πl
10
0
β2
β10
β2.5
β20
β3 β3.5 20
30
40
50
60 t (s)
70
80
90
β30
100
Figure 12: The πΜπ curve of estimation error of ππ .
0
10
20
30
40
50 t (s)
60
70
80
90
100
Figure 14: The ππ curve of PMSM chaotic system added the controller inputs π’π and π’π .
25 50
20 15
40
10 30
5 0
id
π
20
β5
10
β10 β15
0 0
10
20
30
40
50 t (s)
60
70
80
90
100
Figure 13: The π curve of PMSM chaotic system added the controller inputs π’π and π’π .
β10
10
20
30
40
50 t (s)
60
70
80
90
100
Figure 15: The ππ curve of PMSM chaotic system added the controller inputs π’π and π’π .
Figures 5β7 indicate the proposed controller shown in Figures 8-9 can inhibit the external disturbances. Μ πΎΜ, and πΜ Figures 10β12 show the estimated errors πΏ, π of unknown parameters πΏ, πΎ, and ππ for PMSM chaotic system, which testify the effectiveness of constructed adaptive laws and demonstrate the proposed approach has a good robustness against the uncertainties in system parameters.
Γ104
β5.075 β5.08
ud
4.2. Test-II. In reality, the motor parameters are frequently varying with the design values. As a result, the parameters πΏ, πΎ, and ππ in Test-I are changed into πΏ = 0.1, πΎ = 25, and ππ = 1.6 in Test-II, respectively. Simultaneously, the expected reference signals are also changed and set as πβ = 20 and ππβ = 0. In a word, the unknown motor parameters and expected reference signals all differ from Test-I, which is able to validate the proposed control algorithm better. The simulation results are shown in Figures 13β20. Figures 13β15 indicate the motorβs output states π, ππ , and ππ added the
0
β5.085 Γ104 β5.07 β5.075 β5.08 β5.085 β5.09 β5.095
β5.09 β5.095 β5.1 20
46.9 46.92 46.94 46.96 46.98 47
β20
30
40
50
60 t (s)
70
80
Figure 16: The controller input π’π .
90
100
Mathematical Problems in Engineering
11
1000
20 18
500
16 Estimation error of πl
0
uq
β500 β1000 1000
β1500
0
β2000
β1000
30
40
50
10 8 6 4 0
46.9 46.92 46.94 46.96 46.98 47
β3000 20
12
2
β2000
β2500
14
60 t (s)
70
80
90
β2 20
100
30
40
50
60 t (s)
70
80
90
100
Figure 20: The πΜπ curve of estimation error of ππ .
Figure 17: The controller input π’π . 25 0.1
20
0.08
15
Estimation error of πΏ
0.06
10
0.04
5
0.02
π
0
β5
β0.02 β0.04
β10
β0.06
β15
β0.08
β20
β0.1 20
30
40
50
60 t (s)
70
80
90
100
10
20
30
40
50 t (s)
60
70
80
90
100
controller inputs π’π and π’π shown in Figures 16-17, which demonstrate that the designed controller can guarantee the outputs track references well and suppress the external disturbances effectively. Figures 18β20 indicate that the designed adaptive law can estimate the fully unknown parameters precisely even if the fully unknown parameters are changed.
5 0 β5 β10 β15 β20 β25 20
0
Figure 21: The π curve of PMSM chaotic system added the controller inputs π’π and π’π .
Figure 18: The πΏΜ curve of estimation error of πΏ.
Estimation error of πΎ
0
30
40
50
60 t (s)
70
80
90
Figure 19: The πΎΜ curve of estimation error of πΎ.
100
4.3. Test-III. For Test-III, the external disturbances are enlarged in addition to changing the unknown motor parameters and expected reference signals on the basis of Test-II, which are described as Ξ 1 (x, π‘) = 40π₯3 sin(5π‘) and Ξ 2 (x, π‘) = 20 sin(5π‘). The control difficulty in Test-III is larger than the previous two experiments and Test-III is a more general instance to verify the controllerβs performance. The simulation results are shown in Figures 21β28. Figures 21β23 give the curves of the state variables π, ππ , and ππ , which manifest these variables are controlled to their references and chaos is eliminated when adding the proposed controllers
12
Mathematical Problems in Engineering 40 1000 30
500 0
20
β500 β1000
0
10
20
30
40
50 t (s)
60
70
80
90
30
40
50
60 t (s)
70
47.1
β2500 20
100
46.9
β2000
47
β10 β20
1000 500 0 β500 β1000
β1500
47.05
0
46.95
uq
iq
10
80
90
100
90
100
Figure 25: The controller input π’π .
Figure 22: The ππ curve of PMSM chaotic system added the controller inputs π’π and π’π . 50
0.2 0.15
40 Estimation error of πΏ
0.1
id
30 20 10
0.05 0 β0.05 β0.1
0 β10
β0.15 0
10
20
30
40
50 t (s)
60
70
80
90
β0.2 20
100
30
40
50
60 t (s)
70
80
Figure 26: The πΏΜ curve of estimation error of πΏ.
Figure 23: The ππ curve of PMSM chaotic system added the controller inputs π’π and π’π .
5
Γ104 Γ104 β5.075
β5.065
0
β5.07
47.1
47
47.05
β5.075
46.95
β5.085 46.9
ud
Estimation error of πΎ
β5.08
β5.08
β5 β10 β15 β20
β5.085 20
30
40
50
60 t (s)
70
80
Figure 24: The controller input π’π .
90
100
β25 20
30
40
50
60 t (s)
70
80
90
Figure 27: The πΎΜ curve of estimation error of πΎ.
100
Mathematical Problems in Engineering
13
0.04
(2) The simulation results show that the designed controller is able to make the PMSM operate out of chaotic state quickly, and the adaptive laws are established to estimate the unknown parameters accurately. Furthermore, the proposed algorithm can ensure the unknown parameters converge to the actual values fast and restrain the external disturbance effectively.
Estimation error of πl
0.02 0 β0.02 β0.04 β0.06 β0.08 β0.1 20
30
40
50
60 t (s)
70
80
90
100
Figure 28: The πΜπ curve of estimation error of ππ .
(3) The design method in this paper is simple and effective. For PMSM chaotic system with fully unknown parameters, the control variables in proposed approach can be self-adjusted with the changing of system parameters. Therefore, our findings are more practical and more convenient for engineering applications. Future research will discuss the application of the proposed control approach into practical implementation.
Competing Interests π’π and π’π shown in Figures 24-25. Figures 21β23 also illustrate the enlarged external disturbances are restrained by the controllers. The estimation errors of the fully unknown parameters are provided in Figures 26β28, which proves the effectiveness of the adaptive laws again. Remark 5. Previous researches on parameter estimation of PMSM chaotic system mostly assumed that only partial parameters of the system are unknown. The paper takes fully nondeterministic parameters πΏ, πΎ, and ππ into account; it undoubtedly extends the theory of parameter estimation for PMSM chaotic system. Remark 6. The action time of control inputs is 20 s in the simulation. The aim of doing this is to observe the effect of the control approach better. In reality, as long as the chaos occurs, the controller will be put into effect. Remark 7. On the basis of considering fully unknown parameters, the external disturbances are introduced into the PMSM chaotic model. Hence, the designed control consists of two parts. One is to guarantee the state variables to track the reference signals; another is to suppress the external disturbances. In general, the simultaneous consideration of fully unknown parameters and external disturbances makes the research results more general and practical.
5. Conclusions In this paper, a control approach is proposed to address the control issue of chaos in PMSM system with fully unknown parameters and external disturbances. Main conclusions are acquired as the following: (1) Through combination of adaptive control with backstepping control, the presented adaptive robust backstepping control scheme resolves the main problems of the conventional backstepping algorithm encountered. And the stability of the designed controller is proved by Lyapunov theory.
The author declares that there is no conflict of interests regarding the publication of this paper.
Acknowledgments This work is partially supported by the National Natural Science Foundation of China (Grant no. 51407077) and the Fundamental Research Funds for the Central Universities of Ministry of Education of China (Grant no. 2014MS93).
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