Optimal Power Control Model of Direct Driven PMSG

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Energy Procedia 12 (2011) 844 – 848

doi:10.1016/j.egypro.2011.10.111

Available online at www.sciencedirect.com Available online at www.sciencedirect.com

Energy

Procedia

Energy Procedia 00 (2011) 000–000

www.elsevier.com/locate/procedia

ICSGCE 2011: 27–30 September 2011, Chengdu, China

Optimal Power Control Model of Direct Driven PMSG

Cun-Lu Dang, Lei Zhang

*

_{, Ming-Xing Zhou}

College of Electrical and Information Engineering, Lanzhou University of Technology and Key Laboratory of Gansu Advanced Control for Industrial Processes, Lanzhou, 730050, China

Abstract

In order to analyze the performances of direct driven PMSG, an optimal power control model which includes maximum power extraction control model under low wind speed and pitch angle control model under high wind speed is established. The concept of the model is analyzed in a 1.5 MW direct drive variable speed permanent magnet synchronous generator (D-PMSG) WECS with back-to-back IGBT frequency converter. Vector control of the generator side rectifier is realized in the grid voltage vector reference frame. Confirmation of models and control schemes is demonstrated by using the EMTDC/PSCAD environment.

Keywords: Wind energy conversion system (WECS); Perzmanent magnet synchronous generator (PMSG); Maximum power point tracking (MPPT)

1. Introduction

Due to the increasing number of wind turbines installed, the energy production by means of wind power is increasing by approximate 30% annually [1]. Owing to high efficiency, low mechanical loss, and low maintenance cost, the direct driven wind power system including the permanent magnet synchronous generator (PMSG) is drawing people's attention more and more. Mastering the wind generating set's operation character and then improving its operation efficiency are the important issue in the research field of wind power generation.

In this paper, a simple wind speed sensorless MPPT controller for variable speed wind energy conversion system (WECS) is proposed. The proposed method of tracking maximum power point does not require the knowledge of turbine parameters or air density, besides it does not require the knowledge of wind speed. The algorithm requires only the instantaneous turbine angular velocity as its input and generates at its output the maximum power for the vector controlled machine side converter control

* Corresponding author. Tel.: +86-13919190725.

E-mail address: [email protected].

Selection and/or peer-review under responsibility of University of Electronic Science and Technology of China Open access under CC BY-NC-ND license. (UESTC)

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system in order to enable the system to track maximum power point. Performance of the proposed controller is proved by simulation.

2. Variable Speed Wind Turbine Characteristics

The wind turbine characteristics can be described as follows based on Betz theory [2].

(

)

3 0.5 , m P P = ρAv C λ β (1) R v ω λ = (2)

(

,

)

0.22 116 0.4 5 12.5i P i C _{λ β} _β e λ λ − ⎛ ⎞ = ⎜ − − ⎟ ⎝ ⎠ (3) 3 1 1 0.035 0.08 1 i λ =λ+ β β− + (4) m

P -mechanical output power of the turbine (W);ρ -Air density (kg/m3_{);A-Turbine swept area (m}2_);

v-Wind peed (m/s); CP

(

λ β -performance coefficient of the turbine; β -Blade pitch angle (deg);R-turbine ,

)

radii(m); ω -turbine angular velocity (rad/s); λ -Tip speed ratio of the rotor blade tip speed to wind speed. Equation of the wind turbine is shown as:

m e d T T F J dt ω ω − − ∗ = (5) whereT is shaft mechanical torque, m T is electromagnetic torque, F is combined viscous friction of rotor e

and load, J is combined inertia of rotor and load. 3. Maximum Power Point Tracking Control

This paper shows that the 1.5 MW wind turbine is considered. Its power curve with MPPT is shown in

Fig.1, from which it can be seen that, for any particular wind speed, there is a maximum power. When the wind speed changes, the maximum power is controlled to follow the maximum power point trajectory. Note here that precise measurement of wind speed is difficult. Therefore, it is better to calculate the maximum power without measuring wind speed. The manufacturer can change the optimal power curve of the wind turbine by presetting the advanced control system. The purpose of the PMSG power control is that the generator speed can track with the changes of the wind speed, and then the wind turbine generator system can be motioned in the optimal power curve.

Main : Graphs w(p.u.) _0.00 _0.20 _0.40 _0.60 _0.80 _1.00 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 pow er (p. u. ) MPPT

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FORTRAN was the first language to be popularly used by the early researchers, meanwhile it is the oldest language still widely used nowadays. It was designed to express scientific and mathematical formulas and it is still used in those areas. The curve is written by FORTRAN in PSCAD [3].

4. The Control System

The control scheme shown in Fig. 2 (b) is used as the control methodology for the generator side rectifier. Because this rectifier is directly connected to the PMSG, its q-axis current can control the active power. At the same time, the d-axis stator current can control the reactive power. The i instruction is d

usually set as zero.

The control block for the grid side inverter is shown in Fig.2(c).The q-axis current can control the active power .The inside-loop control is the same as generator-side[4],[5].

(a) Electrical scheme of a WECS

abc q i uq d d i Lω d u * d i d i q q i Lω a i b i c i r θ ref P 1 P f ωψ abc dc V iqs * ds i ds i * dc V a i b i c i r θ d e q Li ω d Li ω d e q u d u

(b) Control block diagram of the generator-side rectifier (c) Control block diagram of the grid-side inverter Fig. 2. The control strategy for D-PMSG.

5. Experiments and Analysis

The optimal model has been tested in simulation by EMTDC/PSCAD. The simulated system parameters are listed in the Table 1. In the two typical wind conditions, we can observe the dynamic response and efficiency of WECS with the model.

In the simulation, two wind conditions are involved:

1) Basic wind, a basic wind with 12 m/s which is the rated wind of the WECS lasts 10s. 2) Ramp wind, when t=3s, the wind speed varies from 6 m/s to 9 m/s rapidly;

The simulation results in the above conditions are illustrated from figures 3 to 4 while the pitch angle of wind turbines maintains zero degree and the command value of id is set to be 0.

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Table 1: The Simulation Parameters

Turbine model 3-blade Horizontal Axis

Blade angle β= 0 Air density _ρ₌_{1.225 /}_{kg m}3 Generator parameter 1.5MW D-PMSG Number of poles 36 Rated frequency 10.38Hz Inverter 3MW Double-PWM Grid voltage 690 AC 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.900 11.925 11.950 11.975 12.000 12.025 12.050 12.075 w ind spee d (m /s ) Vw 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 Tur bi ne speed (pu) w

(a) Wind speed (m/s) (b) Turbine speed (rad/s)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 -1.0k -0.5k 0.0 0.5k 1.0k 1.5k 2.0k (k w ) P2 Pref 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 (k V) Udc

(c) Power (MW) (d) DC-link Capacitor Voltage (V)

Fig. 3 Instant response of the novel algorithm (Basic wind). Main : Graphs 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 6.00 6.50 7.00 7.50 8.00 8.50 9.00 w ind speed (m /s ) Vw Main : Graphs 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0.650 0.700 0.750 0.800 0.850 0.900 tur bi ne sp eed (pu) w

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0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 -1.0k -0.8k -0.6k -0.4k -0.2k 0.0 0.2k 0.4k 0.6k 0.8k 1.0k (k w ) P2 Pref 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 (k V) Udc

(c) Power (MW) (d) DC-link Capacitor Voltage (V) Fig. 4. Instant response of the novel algorithm (Ramp wind).

In the basic condition, Fig. 3 shows that when the input wind speed is equal to the rated wind speed, and the generator speed is approximate to the rated speed and it remains stable, the output active power is 1.5 times larger than that of the rated power, meanwhile, the voltage of direct current generatrix is approximate to the reference value 1200V.

In the ramp condition, Fig. 4 shows that when T is 3 seconds, the wind speed of the original 6m/s begins to add up to 9m/s, the generator system will circulate in the maximum wind power capture area, the grid inverter adopts the unit power factor to be controlled, and then the system operation can be seen in Fig4. It can be observed that the per-unit value 0.63 goes up to 0.96, the generator speed gradually rises, the active power output of the system begins to rise inch by inch, and the grid inverter adopts the unit power control . In the dynamic process, the voltage of direct current generatrix remains the reference value 1200V.

6. Conclusion

In this paper, the simulation system which takes the dynamic of wind turbine into account is established, characteristics of PMSG-WT connect to the grid are analyzed, and validity of the established model and optimal power control strategies are demonstrated. Theory analysis and simulation results prove that the model and the control strategy are so efficient that it can be used to practice production.

However, mechanical sensors such as position and speed sensors have some drawbacks, reducing reliability, increasing complexity and cost of the drive system. Therefore, a sensorless control for PM

machinedrives is of the essence for the WECS.

References

[1] T. Ackermann, Wind power in power systems. John Wiley, Ltd, 2005.

[2] Yan Gangui, Wei Zhicheng, Huang he, “Optimal power control of directly-driven permanent magnet synchronous generator wind turbine,” Elcctric machines and control, vol. 13, pp. 56-61, nov 2009.

[3] Manitoba HVDC Research Centre,PSCAD Users Guide V4.2.

[4] Shuhui Li, Timothy A.Haskew and Ling Xu, “Conventional and noel control designs for direct driven PMSG wind turbines,” Electric Power Systems Research., pp.328–338, June. 2009.

[5] Thongam, J.S. Bouchard and P. Ezzaidi, “Wind Speed Sensorless Maximum Power Point Tracking Control of Variable Speed Wind Energy Conversion Systems,” IEEE International Electric Machines and Drives Conference.pp. 1832 – 1837, May 2009

[6] J. Morren, SW.de Hann, “Ride-through of wind turbines with doubly-fed induction generator during a voltage dip,” IEEE Transactions on Energy Conversion, 2005, 20(2), pp. 435-441.

[7] Abbey C., Joos G., “Effect of low voltage ride through (LVRT) characteristic on voltage stability,” IEEE Power Engineering Society General Meeting, Vol. 2, June 12-16, 2005, San Francisco, USA, pp. 1901-1907.