Blade Pitch Angle Controlling of WT for Constant Power Generation Using PMSG

(1)

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

46

Blade Pitch Angle Controlling of WT for Constant Power Generation Using PMSG

1

Saurabh Goel,

²

Durgesh kumar

1

PG Scholar Electrical Engineering Department,SVS University Meerut

2

Assistant Professor Electrical Engineering Department,SVS University Meerut [email protected]

Abstract—Blade pitch angle control technique in Wind Turbine (WT) operation is very urgently require for gaining a constant output torque for stability of WT system. Therefore, accurate and effective controlling technique is described and implemented to attain constant torque of WT. A suitable controlling approach i.e. Proportional-Integral (PI) based blade pitch angle control is designed and considered for performance investigation in terms of torque stability and response time. The proposed system is implemented in MATLAB/Simulink environment. The performance of the system with these control techniques is investigated under variable wind speed conditions such as step and random variations. However, the performance of the system is found satisfactory with the PI controller.

Keywords

—

Wind energy, PI controller, PMSG, Pitch angle control technique, Renewable energy.

I. INTRODUCTION

The demand of electrical energy is full fill by fossil fuels resources so their consumption rate is increasing exponentially also. There is urgent need to explore more alternative energy sources [1]. In this context, the renewable energy (RE) sources such as solar, wind turbine, fuel cell etc, are the best available options. Before the invention of the diesel, petrol and gases etc., wind power was primarily used for applications e.g. sailing ships, irrigation applications etc.

Now-a-days, a research interest is totally focussed on electricity generation through RE sources [2]. Wind power is utilized in various purposes e.g. agricultural activities, water transportation and electricity production etc. [3]. Wind power is reported as the fastest growing RE source in various types of RE sources.

The authors of [4-5] gave a concept on the controlling of wind turbine (WT) using the fuzzy logic controller (FLC) for gaining the maximum power at consumer side. The authors have also shown pitch angle controlling to the WT is suitable for the low level wind speed regions also. In [6], the authors have discussed a WT model and the mechanical torque is produced by the WT. The constant pitch angle of WT has been used for the purpose of electric power generation with

turbine generator system (WTGS) connected with a variable speed turbine generator.

The motivation of above literature review is forced to add the research novelty in this paper. Furthermore, an performance enhancement and comparative study of proportional-integral based control scheme is proposed for blade pitch angle control for torque optimization in WT system.

II. SYSTEM DESCRIPTION

The complete system is comprises mainly three major parts (a) Wind Turbine (b) Permanent magnet synchronous generator (c) Blade pitch angle controlling techniques (i) PI controller. The schematic diagram of complete system is shown in Fig. 1 as,

Fig. 1 Block diagram of blade pitch angle control of WT system.

The paper is scheduled as. In section III, the mathematical modeling of WT is presented. In section IV, PMSG is discussed. In section V, blade pitch angle control scheme is given. Furthermore, the results are reported in section VI and in last section VII concludes the paper briefly.

III. MODELING OF WIND TURBINE

A WT is a system that is used for converting the kinetic energy of wind into mechanical energy. The WT can function at steady speed with changeable blade pitch angle control that allows the system to generate the electrical power.

The wind power is derived in Eq. (1) as, permanent magnet synchronous generator (PMSG), but in 1 3

realistic condition wind has dynamic nature at all regions and Pwind  A



Vw

2 (1)

times. In [7-8], the authors presented the dynamic model of Wind Energy Conversion System (WECS) using PMSG system, and the authors investigated and found that the wind

Where, A is the swept area of WT blades,

 is

the air density and Vw is wind speed (m/s).

PI controller

Error signal





 

_ref

Wind Turbine



_act

Torque

Sensor PMSG

(2)

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

47

i

The power and torque equations of a wind turbine are Where tem is the electromagnetic torque of the expressed in Eq. (2)-(3). The mechanical power (Pm) of the

WT can be calculated as, generator, and id and iq are the currents on d-q axis, and



f is the permanent magnetic flux.

P 1



AC V ³

m 2 ^{p w}

(2) V. B LADE PITCH ANGLE CONTROLLER The mechanical torque is calculated in Eq. (3) as, A. Proportional - Integral controller

T 1



AC V ²R

(3)

m 2 ^{p w}G



^

Where, Cp is performance of coefficient, R is rotor radius, G is gear ratio,



is tip speed ratio (TSR).

The non-linear and dimensionless Cp is expressed in Eq.

(4)-(5) as [10],

The addition of proportional and integral gain increases the speed of the response and also to minimize the steady state error [12]. The block diagram of PI controller is shown in Fig.

2 as,

 ^k⁵

C

 

k k₂

k



k e ^ⁱ  k



 ₍₄₎

p ( , ) 1 



^ ³ ⁴^ ⁶ 1  1

ⁱ 

0.035 (5) Fig. 2 Block diagram of PI controller.

 

0.08

 

³1

The tip speed ratio



is expressed in Eq. (6) as the ratio between the speed of the tips of the blades of a WT and the

The PI controller equation is given in Eq. (13) as,

d



Kpe(t) Ki



^e(t)dt ⁽¹³⁾

wind speed. Where, Kp and Ki are used to control the steady state

V



R



= V^tipw = Vw

(6) response and outputs of the system. The input of the PI controller is the error between Tref and Tactual and the output is Where, ω is the WT blade angular velocity (rad/s),



is

pitch angle of the blade.

The new power coefficient equation is derived in Eq. (7) as [10],

change in blade pitch angle [13, 14].

VI. RESULTS AND DISCUSSION

The proposed system is simulated in MATLAB/Simulink.

The performance of the system under consideration is

116 ^21^0.735 analyzed for the PI controller under different wind speed C_p(



) 0.5176



^ 9.06 e ^ .0068



 (7)

 



IV. PMSG

Permanent magnet synchronous generators are utilized for various commercial purposes in wide range. They are commonly used to convert the mechanical power output of turbines i.e. steam, gas and wind turbines into electrical power [11]. The mathematical model of the PMSG in the state equation form is given by Eq. (8)-(9) as,

condition, pitch angle, turbine torque and PMSG stator currents, rotor speed and electromagnetic torque. All the results are reported as,

 System performance with PI controller for step wind speed pattern

 System performance with controller for random wind speed pattern

A. System performance with PI controller di_d

 1

(R i 



(L  L )i  u ) (8) The transient response of various quantities with PI dt Lds Lls

s d e qs ls q d

controller is shown below for step change wind speed pattern.

The difference of wind speed is shown Fig. 3. The wind is di_q

 1 (R i 



(L  L )i  u ) (9) varied in the range of 11-15 m/s. Both the cases of step

dt L_qsL_ls ^{s q} ^e ^qs ^{ls d} ^q increase and decrease wind speed from reference point are

Where, R is the stator resistance, Ld and Lq are the inductances of the generator on the d and q axis and Lls is the leakage inductance of the generator, and ωe is the electrical rotating speed ( rad/s) of the generator, defined by the Eq. (10) as,

considered. This pattern of wind speed variation is applied to the systems with PI controller.



e  p



g (10)

Where, p is the pole pairs of the PMSG. The electromagnetic torque equation of PMSG is given by Eq. (11) as,

t_em1.5 p((L_dsL_ls)id i_qi_q



f ) (11)

Proportional

Intergral gain Error

T

+ d

-

T_actual

(3)

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

48

Rotor speed (rad/sec) Stator current I (amp) abc 16

10

14 5

0

12 -5

10

0 5 10 15

Time (sec)

-10

0 5 10 15

Time (sec) Fig. 3 Variable wind speed step pattern

When the wind speed pattern as shown in Fig. 3 is applied to the system, the change in pitch angle dβ and according change in torque is shown in Fig. 4(a)-(b) respectively. It is evident from Fig. 4(a) that increase in wind speed results into corresponding increase in pitch angle to maintain the torque at reference value. Similarly decrease in wind speed results into corresponding decrease in pitch angle to keep the torque at reference point. The effectiveness of PI controller is evident from this figure to track reference torque under variable wind speed conditions. The gain of PI controller is obtained using hit and trial method.

13

10 5 0 -5 -10

(a) Stator current Iabc (A)

2 2.002 2.004 2.006 2.008 2.01

Time (sec)

(b) Enlarge view of stator current (A)

12 800

11

600 10

9 400

8

-10

0 5 10 15

Time (sec) (a) Blade pitch angle (⁰)

200

0 5 10 15

Time (sec) (c) Rotor speed (rad/sec)

-15 -10

-20 -14

-25

0 5 10 15

Time (sec)

-18

-2

The stator currents (Iabc), rotor speed and electromagnetic torque of PMSG used in the system with PI conroller are shown in Fig. 5(a)-(d) as,

(d) EM torque of PMSG

Fig. 5(a)-(d) stator current, rotor speed and, electromagnatic torque of PMSG with PI controller.

It is observed from Fig. 6(a)-(c) that stator currents, rotor speed and electromagnetic torque of PMSG are constant with some transient at the time when there is a change in torque.

These transients are settled down quickly under the influence

WT torque (Nm)Blade pitch angle (o) Wind speed (m/s) Stator current I (amp) abc EM torque (Nm)

(b) WT torque (Nm) 2

0 5 10 15

Fig. 4(a)-(b) Transient response of pitch angle and torque with PI controller.

Time (sec)

(4)

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

49

of PI controller used in the system. The overshoot in stator

currents, rotor speed and EM torque at 8 sec is quite significant and observable due to large change in wind speed from 10 m/s to 15 m/s. Fig. 4 to 5 shows the satisfactory performance of considered system with PI controller.

Voltage, current and power at 3-phase resistive load is shown in Figure 7(a)-(c) as,

2000

1000

0

12

10

8

6

4

0 5 10 15

Time (sec) Fig. 8 Variable wind speed pattern

-1000

-2000

10 5

0 -5 -10

0 5 10 15

Time (sec) (a) Load voltage (V)

When the random wind speed pattern as shown in Fig. 8 is applied to the system, the change in pitch angle dβ and according change in torque is shown in Fig. 9(a)-(b) respectively. It is evident from Fig. 9(a) that increase in wind speed results into corresponding increase in pitch angle to maintain the torque at reference value. Similarly decrease in wind speed results into corresponding decrease in pitch angle to keep the torque at reference point. The effectiveness of PI controller is evident from this figure to track reference torque under variable wind speed conditions. The gain of PI controller is obtained using hit and trial method.

-0.8

-0.85

0 5 10 15

Time (sec) (b) Load current (A)

-0.9

-0.95 12000

8000 4000 0 -4000 -8000 -12000

0 5 10 15

Time (sec) (c) Load power (W)

-1

-12

-13

-14

0 5 10 15

Time (sec) (a)

Fig. 7(a)-(c) Load voltage, current and power

B. System performance with PI controller for random wind speed pattern

The transient response of various quantities with PI controller is shown below for random change wind speed

-15

-16 0 5 10 15

Time (sec) (b) WT torque (Nm) pattern. The difference of wind speed is shown Fig. 15. The

wind is varied in the range of 5.8-11.7 m/s. Both the cases of step increase and decrease wind speed from reference point are considered. This pattern of wind speed variation is applied to the systems with PI controller.

Fig. 9(a)-(b) Transient response of pitch angle and WT torque

The stator currents (Iabc), rotor speed and electromagnetic torque of PMSG used in the system with PI controller are shown in Fig. 10(a)-(c) as,

Load power (watt) Load voltage (volt) Load current (amp) Wind speed (m/s) Blade pitch angle (o) WT torque (Nm)

(5)

50

10

5

0

-5

-10 0 5 10 15

Time (sec) (a) Stator current Iabc (A)

constant with low transient at the time when there is a change in torque. The transients are very low under the influence of PI controller used in the system. This random wind speed pattern is not effective on PMSG performance.

Voltage, current and power at 3-phase resistive load is shown in Figure 11(a)-(c) as,

1000 500

0 -500 10

-1000 5

0

0 5 10 15

Time (sec) (a) Load voltage (V)

-5

-10

350 340 330 320

1 1.002 1.004 1.006 1.008 1.01 Time (sec)

(b) Enlarge view of stator current Iabc (A)

5

0

-5

0 5 10 15

Time (sec) (b) Load current (A)

310

300 0 5 10 15

Time (sec) (c) Rotor speed (rad/sec)

4000

2000

0

-14 -14.2 -14.4 -14.6 -14.8

-2000

-4000

0 5 10 15

Time (sec) (c) Load power (W) Fig. 18(a)-(c) Load voltage, current and power

VII. CONCLUSIONS

-15 0 5 10 15

Time (sec) (d) EM torque (rad/sec)

In this paper, a study of WT based WECS has been carried out. The real value system model of WT along with the system components are built in MATLAB/Simulink environment. With the simulation of the complete WECS Fig. 10(a)-(d) Stator current, rotor speed and, EM torque of PMSG with PI

controller.

It is observed from Fig. 10(a)-(c) that stator currents, rotor speed and electromagnetic torque of PMSG are almost

using MATLAB/Simulink model, all the results have been obtained for PI based controller. A comparative study of step change and random pattern of wind speed is done for the system.

Rotor speed (rad/sec) Stator current I (amp) EM torque (Nm) Stator current I (amp) abc abc Load power (watt) Load voltage (volt) Load current (amp)

(6)

51

The simulation results shows that the reference torque is

conveniently achieved by adjusting the blade pitch angle by PI based controller. It is observed that the small random change in wind speed is less disturbed to the WT system in compare to the step change pattern of wind speed.

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