Modeling and Simulation of PMSG using SVPWM ...

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 6 (2015) © Research India Publications ::: http://www.ripublication.com

Modeling and Simulation of PMSG using SVPWM switching Technique 1

V.Meenakshi, 2 S.Paramasivam 1Assistant Professor-EEE Department, Sathyabama University, Jeppiaar Nagar, Chennai-600 119, India 2.R&D Head, ESAB Group, Sriperumpudur Taluk, Kanchipuram District, 602 105, India

Abstract Renewable energy production and demand growth is can also be obtained by using Power electronics devices in an gaining momentum in many ways across the world. There is a intelligent control method [3]. Generally the wind energy system model is shown in Fig.1, roaring demand of wind power today and all wind energy which includes models of wind, turbine, drive train and, PMSG equipment manufacturers are gearing up to meet the demand and take advantage of it. Here the various control strategies in and control system model [4]. The first three models describe the wind electric generation are modelled and the related the mechanical parts of wind turbine, generator model scopes are outlined using Matlab. This paper intends in representing the electromechanical link and last, the control bringing maximum power by using proper switching technique system model controlling the generator output. The total wind to enhance the power production by proper tracking of rotor velocity is the combination of base wind velocity, gust wind speed and controlling the duty ratio of power converters. There component and ramp wind component [5]. Earlier proposed switching techniques have at least one of is a growing trend of using space vector pulse width modulation switching techniques because of their reduced total the following drawbacks and limited their extensive use. 1. They are implemented SVPWM technique with harmonic distortion. FPGA which is expenditure wise more [6]. 2. The switching technique used for inverter fed Induction motor is SPWM which has more total Keywords: power electronic converter, PMSG, SVPWM, Harmonic distortion [7], [8], [9]. wind electric generator WEG. 3. Researchers have tried to model and simulate the Ultra Large wind turbine without considering the 1. Introduction Switching Techniques [10]. As fossil fuels continue to diminish and climate change 4. Harmonic reduction are not taken into consideration poses an ever-increasing warning, scientists all around the [11], [12]. world are searching for new and more efficient methods of This paper presented SVPWM switching technique that generating energy. Wind energy is one of the more promise overcomes the above drawbacks. This paper is written in a alternative energy source and hottest thing on the promote right lucid manner that Section II outlines the modeling of PMSG in now[1].Wind turbines are frequently touted as the answer to wind energy system. Section III describes the SVPWM control sustainable electricity production especially if coupled to highstrategies on wind electric generator and the corresponding capacity storage for times when the wind speed is either side of results. Section IV shows PMSG in MATLAB/SIMULINK. their working range. Wind source offers essentially zero carbon Section V includes the wind electric power generation using emissions. Coupled lifecycle cost and environmental SVPWM used in it ends with a concluding remark that wind assessment in terms of energy use and emissions of power wins through other power generation shortly. manufacturing, maintenance, installation, and turbine end-oflife processing seems to be limited in the discussions for and against these devices. All form of energy generation require the conversion of natural resource inputs, which are assistant with 2. Modeling and Description of PMSG ecological impacts and costs that must be quantified to make 2.1Synchronous Machines appropriate energy system development decisions. Research on dynamic models for grid-connected as well as stand-alone wind energy conversion systems is one of The synchronous machines have many advantages over the challenges to achieve knowledge for the ongoing change due induction machines. One of them is a high efficiency. In to the intensification of using wind energy nowadays. The induction machines reactive power for rotor excitations carried amount of energy obtained from a wind energy conversion by stator winding as well as the active power for conversion. so system (WECS) depends not only on the characteristics of the synchronous generators will have better efficiency and better wind system at the site, but it also depends on the control power factor. In variable speed wind system, the synchronous strategies used in it [2]. In order to get the greater power from generators are connected to the Grid via a power electronics the wind, the wind turbine should run at different speed when converter. The quantity of deliverable active power from Synchronous Generator (SG) depends on rating ofa converter in wind speed changes. The optimum power

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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 6 (2015) © Research India Publications ::: http://www.ripublication.com

Volt-Amperes and the power factor of SG. Thus, for the same evaluation of the converter, IF the Power factor gets to unity; the more active power can be delivered. Moreover the rotor speed does not depend on the electrical load conditions. In wind system it is more suitable to control the rotor speed merely based on the Wind speed. The other benefit is that they can have longer air gaps compared to induction machines. In induction machines, the air gap length is kept small to limit the magnetization current and to improve the power factor. In synchronous Machines, because of longer air gap it helps to reduce armature reaction and the synchronous reactance which in turn improves the stability.

maintenance. Mechanical susceptibility of rotor windings arising from rotation leads to winding insulation damage. 2.3Permanent Magnet Synchronous Generator

Self-excitation brings about various benefits. The exclusion of the rotor copper losses is one of the benefit. Hence PMSG s are more competent compared to WRSG s. The safeguarding is eliminating since brushes and slip rings as well as the rotor windings are removed. The common problem with WRSG is the relation between the frequency induced and the mechanical speed of the rotor. According to the change in wind speed the rotor speed and thereby the frequency of the induced voltage changes. However, in variables speed applications with PMSG this is usually not of concern since the generator is connected to the grid through a converter that will adapt the frequency of the induced voltage to the grid frequency. Solitary other consideration is that, not like WRSG, the magnetic field cannot be controllable. It is not possible to control the voltage and the reactive power. In changeable speed wind systems the output voltage and the power factor is determined by the grid-sideconverter. A maintenance requirement is low and thus lower cost is the main reasons why PMSGs are proposed with variable speed wind systems. Yet another problem that needs to be Fig.1.Schematic of typical wind electric system measured is the risk of demagnetization of magnets due to the temperature rise; the magnets can be partially or fully demagnetized. In partial demagnetization the magnetic properties are weakened. In full demagnetization magnetic Fixed speed wind systems with SG have the same disadvantages properties are completely lost and they require magnetization as their IG counterpart. In addition, there is also need for starting which is a tedious task and in some cases impossible and anew and synchronizing equipment too. The importance of a variable rotor is required. Thus a thermal study is suggested to promise speed wind systems equipped with a SG lies in their capability that the magnet working temperature is, in any conditions, to meet the aerodynamic requirements in the widest speed range. conserved low. Additionally, the partial demagnetization is To keep the tip speed ratio at its optimal, the wind turbine rotor usually a case during a short circuit where some parts of the speeds vary proportional to the wind speed. This provides rotor magnets are exposed to high opposing magnetic fields. In it is speed independency from load conditions. Wide operational shown that PMSG’s are more suitable for gearless applications speed range, from zero to rated speed, is beneficial for control compared to WRSG’s. In comparison of PMSG and WRSG and purposes. Functioning advantages of a SG with power varying the number of poles, it can be shown that once the electronics converters are several, for example voltage number of poles reaches high values, the rotor yoke height of regulation which is handled by the grid-side converter. WRSG becomes thicker. Consequently, weight and size of Another advantage is that dynamic disturbances of the grid WRSG surpasses that of PMSG. and the wind turbine are isolated from each other and SG is not at risk of losing synchronism. Furthermore, starting and 2.4 Model of PMSG synchronizing equipment is not needed as this is taken care of by power electronics converter. The only gain of IGs over SGs is The voltage equation for PMSG kept in synchronous that the converter is not dimensioned for full control. However, reference frame is given by with latest decrease in cost of power electronic components, this is not of anxiety anymore. di

Vd  Rs ids  Ld s

2.2Wounded Rotor Synchronous Generator Wounded Rotor Synchronous Generator (WRSG) s have been scope of research for many years. The main improvement of WRSG over PMSG is that it intrinsically can produce reactive power and subsequently regulate the voltage. Thus power factor can be controlled to electrical load conditions. The reactive power is injects to compensate loads reactive power consumption. However the WRSG has not gained recognition among the wind turbine manufacturer. It is mainly for the reason that that the brushes for DC excitation in WRSG require

Vq  Rs iqs  Lq s

ds

dt diqs dt

  e Lqs iqs

(1)

  e Lds i ds   e (2)

The current equations for PMSG model can be written in d-q synchronously rotating frame by

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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 6 (2015) © Research India Publications ::: http://www.ripublication.com

3. SVPWM Control Strategies

Lqs v R d ids  d  s ids  pwr i qs dt Lds Lds Lds

(3)

vq R L pwr d i qs   s iqs  ds pwr ids  dt Lqs Lqs Lqs Lqs

(4)

The general block of SVPWM consist of seven blocks, they are three phase generator, low-pass bus filter, alpha beta transformation, αβ vector sector, ramp generator , switching time calculator , gates logic. The three-phase generator gives the inverter demanded frequency and voltage is two of the block inputs. The three –phase generator produce three sine waves with variable frequency and amplitude. The three signals are out of phase with each other by 120 degrees. The voltage equations are

The torque equation for PMSG is given by

Te  1.5 p( Lds  Lqs )ids iqs  i q 

Vr=Vmsinωt Vy=Vmsin (ωt-2π/3) Vb=Vmsin (ωt-4π/3)

(5)

(6) (7) (8)

Where Lds and Lqs are d and q axis inductance, Rs is stator resistance winding, P is number of pole pairs Wr is angular velocity of rotor, ¢ is amplitude of flux. The equivalent circuit of PMSG based on WECS in When a three phase supply is applied to the windings of a threeFig. 2. The conventional model of PMSG in the d-q phase ac machine, it leads to a revolving resultant voltage space vector. The resultant voltage space-vector will be revolving synchronous reference frame as shown in Fig. 2a and Fig. 2b. consistently at the synchronous speed and will have a magnitude equal to 1.5 times the peak magnitude of the phase voltage. For the duration of each time period of the phase voltages six discrete time instants can be known, and it is shown in Fig. 3.Each phase voltage is having maximum positive or negative instantaneous magnitude. The voltages at the instants are named as V1 to V6.

Fig.3.Resultant three phase voltage space vector The output pattern of the three phase voltage source inverter i.e instantaneous voltage matches the six discrete instants of the three phase voltage space vector. In three phase voltage space vector one of the phase voltage is positive and other two are negative and vice versa .One of the phase voltages have positive or negative peak level and the other two have half of the peak level.

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g

C

g

C

C

g

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 6 (2015) © Research India Publications ::: http://www.ripublication.com

C+

a+

E

E

E

b+ 3-phase load

g

C

g

C

C

g

Vdc

CE

E

E

b-

a-

Fig.4.Voltage Source Inverter Fig. 4 shows a three-phase voltage source inverter .It consists of six switches ,out of six three switches are upper side switch and Fig. 5 .The voltage space-vector plane formed by the it is indicated as ‘1’ when it is on, and remaining three switches Active state are lower side switch and it is indicated as ‘0’ when it is on. Thus the six switches of the three legs will have a total of eight The resultant voltage vector can be attained by accurately different switching combinations. The two switches of each governing the stay times of two adjacent active voltagevectors inverter leg conduct in a complementary manner. Out of these and null voltage vectors. The two active state vectors chosen are eight combinations, two combinations are zero output voltage the ones that define the boundary of the space-plane sector in and it is said to be inactive state and remaining six combinations which the desired resultant vector lies. The following illustrative are said to be active state and gives output voltage. Switching example may be helpful. states of the inverter have been indicated by a 3-bit .The Example: switching states are indicated in table 1. Let us assume that a resultant vector ‘VR’ of magnitude α(Vdc), lying in sector-1and making an angle ‘θ’ from active vector V1 is to be realized Fig. 6. Let us further assume that ts are the 3.1Efficientlyrevolving Space Voltage Vector from Inverter sampling time for which the desired vector VR may be assumed to be stationary in space along the described direction. Now as The convenient power electronics inverter does not produce per the above discussion the desired vector is to be realized using perfectly ideal sinusoidal voltages. So space-vector PWM active vectors V1, V2 and null vectors V7, V8. Let the respective technique is used. The six active state voltage vectors are dwell time along these vectors be t1, t2, t7 and t8 such that indicated as V1 toV6 (101,100,110,010,011,001) and have a t1+ t2 + t7 + t8 = ts (9) magnitude of Vdc.The two inactive state voltage vectors are indicated as V7, V8 (000,111), it is at the origin of the voltage vector plane. Fig. 5 shows the voltage space-vector plane formed v1 by the active state and null state voltage vectors. The six active state voltage space vectors are joined to form a hexagon and it is v2 divided into six identical zone(1-6).The output voltage vector vR from the inverter (barring high frequency disturbances) should be rotating with fixed magnitude and speed in the voltage plane and null state voltage vectors. θ Fig.6.Resultant output voltage Space-vector

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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 6 (2015) © Research India Publications ::: http://www.ripublication.com Line to Line voltage

Voltage vector

Switching vector

a+

b+

c+

a-

b-

c-

V0 V1 V2 V3 V4 V5 V6 V7

000 100 110 010 011 001 101 111

OFF ON ON OFF OFF OFF ON ON

OFF OFF ON ON ON OFF OFF ON

OFF OFF OFF OFF ON ON ON ON

ON OFF OFF ON ON ON OFF OFF

ON ON OFF OFF OFF ON ON OFF

ON ON ON ON OFF OFF OFF OFF

of

3-

Table.1.Switching

states t1

( v1)

t2

(v2)

The resultant space vector is sum of t s and t s V1 and V2 space – vector having a magnitude of Vdc.

, where

phase

Vab 0

Vbc

Vca 0

0 0

+V dc

-V dc -V dc

+V dc +V dc

0 -V dc -V dc

0 +V dc +V dc

0

+V dc

-V dc -V dc

0

0

0

voltage

0 0

source

inverter.

Obtained from subsystem 2.The output of the inverter is given to three phase load. N

Flux*

N*

Torque*

1500

The vector algebra is given as

Torque* Ma gC

Speed reference3 MagC

Speed refe rence

3

Flux*

speedctrl1

V_abc

Ctrl

Subsystem

Gates

I_ab

t t    1 cos   2 cos(   ) ts ts 3

p owergui

Scope1

DIRECT TORQUE CONTROL

Discrete, Ts = 1e-00 6 s.

Scope [AsyncMac_sig]

Load torque

Rate Transition RT

Measures

g Meas.

+

V L-

-

V L+

V+

V-

[AsyncMac_sig]

A

Ta

B

Tb

Tm

C

Tc

I_ab V_abc Mta Mtb V_Com Mtc

A



m B

THREE PHASE INVERTER



C A

B

B

C

C

+

BRAKING CHOPPER

N

Goto2

THREE PHASE DIODE BRIDGE RECTIFIER

Freq*

Freq*

Volts*

Volts* gates dir

dir N* ctrl

1800



1/z

Rad/s2Rpm

-K-



Vdc Bus

4 Ctrl

Subsystem1

Speed reference1



Goto1

Scope3

[Pulses_rotor_conv] [Pulses_rotor_conv]

V+ V-

Meas ures 1



-T -

Subsystem2

Vabc A

(11)

Iabc

A

g

g +

The maximum voltage magnitude α along the θ is given as

B

aB

A

C

b

B

Three-Phase Parallel RLC Load

From equations (10) and (11) we can determine the sampling time during which the inverter is along the active time v1 and v2.

c

+ A

Vabc

-

C

C

Universal Bridge

Universal Bridge1

c

1/z

1 Pitch_deg

1/z

[Qmeas]

1/z

[Pitch_deg]

P_pu

W_wt (pu)

2 Pitch angle (deg)

PQ_pu

Tt (pu)

T_wt (pu)

W_wt (pu)

Wind speed (m/s) Generator speed (pu)

-K-

T_shaft (pu)

Wind Turbine 12

Power base for the Generator

Drive Train

Constant 1500 Speed reference2 [Wr]

wr

Tem_cmd

Pmeas

Pitch (deg)

[Tem_cmd]

[Pitch_deg]

[Pmeas]

(12)

PITCH CONT ROL

The process continues to produce a continuously rotating voltage space vector of fixed magnitude and fixed speed.

Fig.7.PMSG based WECS using SVPWM Technique

4. PMSG in MATLAB/SIMULINK Using SVPWM Control Techniques. Fig .7.shows a three phase 460v,60 Hz ac source is given to a rectifier ,the output of the rectifier is given to the breaking chopper than to a 3 phase inverter ,the gate pulse which is given to the inverter is obtain from direct torque control block. The direct torque control block generate the gate pulse depend up on the torque and flux. The inverter output is fed to 300v, o.8 Nm, 3000 rpm permanent magnet synchronous machine .The mechanical torque is generated from turbine and drive train blocks than applied to the machine shaft. The rotor speed is given to the subsystem1 (speed controller).The speed controller block compares the rotor speed and reference speed and gives the output to subsystem2 (svpwm block).The inverter required voltage and frequency is

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Fig.8.PMSG Stator current abc.

C

B_rotor_conv

Turbine and Drive Train

[Pitch_deg]

[Pmeas]

A

a B b

B

C1 -

C

B_grid_conv

Q_pu

 sin( ) 3   sin(   )  sin  3

Scope2



[Wr]

-

460V 60Hz

t1 t  sin   2 sin(   ) ts ts 3



300v, 3000rpm,0.8 Nm Permanent magnet synchronous machine

V bu s

(10)

A

[Tm]

[Vabc_rotor]

Scope4

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 6 (2015) © Research India Publications ::: http://www.ripublication.com

4.1 FFT ANALYSIS FOR SVPWM FFT analysis for PMSG stator current, stator voltage, rotor speed, rotor angle thetam, electromagnetic torque is shown in Fig.12, 13, 14, 15.

Fig.9.PMSG Stator voltage dq

Fig .12.FFT analysis for PMSG stator current

Fig.10. PMSG Stator current qd

Fig.13.FFT analysis for PMSG Electromagnetic torque

Selected signal: 18 cycles. FFT window (in red): 1 cycles 500 0 -500 0

0.05

0.1

0.15 Time (s)

0.2

0.25

0.3

M ag (% o f F u nd a m e n t al)

Fundamental (60Hz) = 305 , THD= 107.05%

Fig.11. PMSG rotor speed (rad/s), rotor angle thetam (rad), Electromagnetic torque (Nm) by using SVPWM technique.

40 30 20 10 0

0

100

200

300

400 500 600 Frequency (Hz)

700

800

900

1000

Fig.14.FFT analysis for PMSG Voltage qd.

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[2] Nitin Adhav, Pg Student Shilpa Agarwal, ‘Comparison and Implementation of Different PWM Schemes of Inverter in Wind Turbine’, International Journal of Innovative Technology and Exploring Engineering (IJITEE) ISSN: 22783075, Volume-2, Issue-2, January 2013. [3] Agustina Hernandez, Ruben Tapia, Member, IAENG, Omar Aguilar, and Abel Garcia, ‘Comparison of SVPWM and SPWM Techniques for Back to Back Converters in PSCAD’, Proceedings of the World Congress on Engineering and Computer Science 2013 Vol I WCECS 2013, 23-25 October, 2013, San Francisco, USA [4] Wind Turbine design, Wikipedia, The free Encyclopedia [5] P.Srinivas and M.L.S.Devakumar, ‘Optimization of Power Factor and Energy Management in Wind Energy Station’, International Journal of Computer Communication and Information System (IJCCIS)– Vol2. No1. ISSN: 0976–1349 July – Dec 2010.

Fig.15.FFT analysis for PMSG Stator currentqd.

S.No 1. 2. 3. 4. 5. 6. 7.

Simulation Results For PMSG Stator Current abc in A Stator Current q axis in A Stator Current d axis in A Stator Voltage qd axis in V Rotor Speed(rad/s) Rotor angle thetam(rad) Electromagnetic torque(Nm)

THD in % SVPWM 75

80.65

70

96.30

18

96.30

400

107.05

-200 -40

47.29 47.29

18

47.29

[6]R.Rajendran and Dr.N.Devarajan, ‘FPGA Implementation Of Space Vector PWM Technique for Voltage Source Inverter Fed Induction Motor Drive’, 2009 Second International Conference on Computer and Electrical Engineering. [7]Palak G.Sharma, S.Rangari, ‘Simulation of Inverter Fed Five Phase Induction motor’, International Journal of Science and Research (IJSR), India, Vol2 issue2, ISSN:2319-7064, February 2013. [8]C.S.Sharma and Tali Nagwani, ‘Simulation and Analysis of PWM Inverter Fed Induction motor drive’, International Journal of Science, Engineering and Technology Research (IJSETR), Volume 2, Issue 2, ISSN: 2278- 7798, February 2013. [9]Raiu.N.I, Islam.M.S, Ali.T, Karim.S.A, ‘Study of SPWM Technique simulation of designed analog circuit (Op-Amp) Controlled three phase PWM inverter with harmonic Reduction PWM inverter with harmonic reduction, Information, Electronics&Vision (ICIEV), 2013 International Conference on IEEE.

Table.2.Simulation Results for PMSG using SVPWM technique.

5. Conclusion In this paper the maximum Power Optimization is obtained from wind energy by implementing suitable switching technique like SVPWM .By using this switching technique the total harmonic distortion can be reduced .This switching technique has proved numerous benefits over the conventional PWM technique and has been confirm to be inherently generating superior PWM technique.Table.2.shows the simulated results for stator current, stator voltage, rotor speed, rotor thetam angle, electromagnetic torque PMSG using SVPWM control switching techniques References [1] Fatehbir Singh, Shakti Singh, ‘Wind Energy Stabilization Using SVPWM Based Modulated Power Filter Compensator’, International Journal of Research (IJR) Vol-1, Issue-6, July 2014 ISSN 2348-6848.

[10] Ahmed M.Hemeida, wael A.Farag and Osama A.Mahgoub, ‘Modeling and Control of Direct Driven PMSG for Ultra Large Wind Turbines’, World Academy of Science, Engineering and TechnologyVol: 5 2011-11-27. [11] S. Samanvorakij and P. Kumkratug, ‘Modeling and Simulation PMSG based on Wind Energy Conversion System in MATLAB/SIMULINK’, Proc. of the Second Intl. Conf. on Advances in Electronics and Electrical Engineering — AEEE 2013, ISBN: 978-981-07-5939-1. [12]Alejandro Rolan', Alvaro Luna, Gerardo Vazquez, Daniel Aguilar, Gustavo Azevedo, ‘Modeling of a Variable Speed Wind Turbine with permanent Magnet Synchronous Generator’, IEEE International Symposium on Industrial Electronics (ISlE 2009) Seoul Olympic Parktel, Seoul, Korea July 5-8, 2009.

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