Grid-Connection Control and Simulation of PMSG Wind Power System Based on Multi-Level NPC Converter

IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 07, 2014 | ISSN (online): 2321-0613

Grid�Connection Control and Simulation of PMSG Wind Power System Based on Multi�Level NPC Converter Sandeep Kumar Gautam1 K P Singh2 1 M.Tech Student 2Associate Professor 1,2 Department of Electrical Engineering Abstract— This dissertation proposes a wind energy conversion system is composed of a wind turbine PMSG, a rectifier, and an inverter. The wind turbine PMSG transforms the mechanical power from the wind into the electrical power, while the rectifier converts the AC power into DC power and controls the speed of the PMSG. The controllable inverter helps in converting the DC power to variable frequency and magnitude AC power. With the voltage oriented control, the inverter also possesses the ability to control the active and reactive powers injected into the grid. Multilevel inerter is used to step up the voltage and to reduce the THD. Here nine level and eleven level inverter are used and the voltage increases and THD reduces from 12.87 % to 7.46 %. Active and reactive power is controlled dc stabilization and the reactive power is near to unity Here PI controller is used to control the inverter output rms voltage and LC filter is used to remove the harmonics available in the system.

Key words: Multilevel inverter, Voltage source inverter, matlab Simulink, rectifier

A. Modeling Of Permanent Magnet Synchronous Machines Permanent magnet synchronous machines/generators (PMSM/PMSG) direct-drive wind power generation system term for transforming the mechanical power into electrical power. A rigorous mathematical modeling of the PMSG is the

I. INTRODUCTION Many industrial applications have begun to use high power apparatus in recent year. Medium power motor drives and utilities require medium voltage and higher power level. In a medium voltage grid, connecting only one power semiconductor switch directly will create problem. To overcome this problem, a multi level inverter topology has been introduced as an alternative in medium voltage and high power situations. A multilevel inverter use renewable energy as source and can achieve high power rating. So, renewable energy sources such as solar, fuel cells and wind can be easily interfaced to a multilevel inverter structure for a high power application. The multilevel inverter concept has been used since past three decades. The multilevel inverter begins with a three-level inverter. Thereafter, many multilevel inverter topologies have been developed.

However, the main concept of a multilevel inverter is to achieve high power with use of many power semiconductor switches and numerous low voltage dc sources to obtain the power conversion that lookalike a staircase voltage waveform. The dc voltage sources for multilevel inverter are given by battery, renewable energy and capacitor voltage sources. The proper switching of the power switches combines these multiple dc sources to achieve high power output voltage. The voltage rating of the power semiconductor devices depends only upon the total peak value of the dc voltage source that is connected to the device. Three major classification of multilevel inverter structures [1-3] are cascaded H-bridge inverter with separate dc source, diode clamped (neutral-clamped), and flying capacitor (capacitor clamped).

Fig. 1: Cross-section view of the PMSM II. POWER AND TORQUE ANALYSIS OF A PMSM For any PMSM, the electrical power input can be expressed in the abc reference frame as follows: đ?‘ƒđ?‘Žđ?‘?đ?‘? = đ?‘Łđ?‘Žđ?‘ đ?‘–đ?‘Žđ?‘ + đ?‘Łđ?‘?đ?‘ đ?‘–đ?‘?đ?‘ + đ?‘Łđ?‘?đ?‘ đ?‘–đ?‘?đ?‘

(1)

or in the dq-axes reference frame as follows: 3

đ?‘ƒđ?‘‘đ?‘ž = (đ?‘Łđ?‘‘đ?‘ đ?‘–đ?‘‘đ?‘ + đ?‘Łđ?‘žđ?‘ đ?‘–đ?‘žđ?‘ )

(2)

2

As a part of the input power, in the motoring mode, the active power is the power that is transformed to mechanical power by the machine, which can be expressed as follows: 3

đ?‘ƒđ?‘’đ?‘š = (đ?‘’đ?‘‘ đ?‘–đ?‘‘đ?‘ + đ?‘’đ?‘ž đ?‘–đ?‘žđ?‘ )

(3)

2

Where đ?‘’đ?‘ž = đ?‘¤đ?‘’ đ??żđ?‘‘ đ?‘–đ?‘‘đ?‘ + đ?‘¤đ?‘’ ∅đ?‘&#x; = đ?‘¤đ?‘’ ∅đ?‘‘ (4)

đ?‘’đ?‘‘ = −đ?‘¤đ?‘’ đ??żđ?‘ž đ?‘–đ?‘žđ?‘ = −đ?‘¤đ?‘’ ∅đ?‘ž

(5)

Here,đ?‘’đ?‘‘ and đ?‘’đ?‘ž , are the back EMFs in the dq-axes reference frame, and ∅đ?‘‘ and ∅đ?‘ž are the dq-axes flux linkages. Substituting expressions (4) and (5) into (3), the active power can be re-expressed as follows: 3

đ?‘ƒđ?‘’đ?‘š = đ?‘¤đ?‘’ (∅đ?‘‘ đ?‘–đ?‘žđ?‘ − ∅đ?‘ž đ?‘–đ?‘‘đ?‘ ) 2

(5)

Hence, the electromagnetic torque developed by a PMSM can be deduced as follows: �� =

đ?‘ƒđ?‘’đ?‘š đ?‘¤đ?‘’ đ?‘?

2

3 đ?‘?

= ( ) (∅đ?‘‘ đ?‘–đ?‘žđ?‘ − ∅đ?‘ž đ?‘–đ?‘‘đ?‘ ) 2 2

(6)

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Grid� Connection Control and Simulation of PMSG Wind Power System Based on Multi � Level NPC Converter (IJSRD/Vol. 2/Issue 07/2014/021)

III. MULTILEVEL INVERTER

A. Simulink Model of Wecs

Multilevel inverter is best suited in power sector. It is used as to control the active and reactive power of grid .In the grid control system multilevel inverter is used to (1) The stability of dc voltage.

(2) Inverter power factor is unity.

(3) Input current contain low harmonics [4].

The general function of multilevel inverter is to synthesize the dc voltage source. Multilevel inverter have capability to increase the high step up voltage without the use of transformer [5]-[9].

By choosing appropriate angle of multilevel inverter we can eliminate the harmonics in a specified output waveform. The necessary conduction angle can be calculated by choosing appropriate phase voltage the output voltage Va0 can be given as [10]-[13]:đ?‘‰đ?‘Žđ?‘œ = đ?‘‰đ?‘Ž1 + đ?‘‰đ?‘Ž2 +Vđ?‘Ž3 +Vđ?‘Ž4 +‌

(7)

Since the waveform is symmetrical to X-axis hence the Fourier coefficient An and Ao become zero. Hence only the analysis of Bn is perform: The standard Fourier series equation are given below ∞

đ?‘“(đ?‘Ľ) = đ?‘Ž0 + ∑

đ?‘›=1

(đ?‘Žđ?‘› cos

đ?‘›đ?œ‹đ?‘Ľ đ??ż

+ đ?‘?đ?‘› sin

đ?‘›đ?œ‹đ?‘Ľ đ??ż

)‌

Fig. 3: Simulink model of wind energy conversion system

(8)

in term of Bn the equation can be written as: đ??ľđ?‘› = (

4đ?‘‰đ?‘‘đ?‘? đ?‘›đ?œ‹

) ∑∞ đ?‘—=1 đ??śđ?‘‚đ?‘†(đ?‘›đ?›źđ?œ… )‌

(9)

j = no. Of dc source n= no of odd harmonics đ?›źđ?œ… = switching angle of level k By solving above equation (3) đ?‘—đ?‘€ 4 cos 3đ?›ź1 + cos 3đ?›ź2 + â‹Ż + cos 3đ?›źđ??ž = 0

Fig. 4: Simulink model of wind turbine

cos đ?›ź1 + cos đ?›ź2 + â‹Ż ‌ ‌ . cos đ?›źđ?‘˜ =

cos 5đ?›ź1 + cos 5đ?›ź2 + â‹Ż + cos 5đ?›źđ??ž = 0 The above equation can be solved by using Newton Raphsonmethod to find switching angle.

Fig. 5: wind speed at 12 m/sec

Fig. 2: Simulink model of full circuit Fig. 6: waveform of wind turbine at 12 m/sec wind speed

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Grid� Connection Control and Simulation of PMSG Wind Power System Based on Multi � Level NPC Converter (IJSRD/Vol. 2/Issue 07/2014/021)

Fig. 7: Stator current of PMSG

Fig. 10: Simulink model of nine level inverter B. Simulation Results Of Nine Level Inverter Fig. 8: Simulink model of generator terminal

Fig. 9: Dc link Voltage

Fig. 12: phase voltage waveform of nine level inverter

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Grid� Connection Control and Simulation of PMSG Wind Power System Based on Multi � Level NPC Converter (IJSRD/Vol. 2/Issue 07/2014/021)

Fig. 17: FFT analysis of nine level inverter Fig. 14: phase voltage waveform

Fig. 18: Simulink model of eleven level inverter Fig. 15: line voltage of nine level inverter

C. Simulation Result Of Eleven Level Inverter

Fig. 16: line voltage waveform

Fig. 19: phase voltage waveform

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Grid� Connection Control and Simulation of PMSG Wind Power System Based on Multi � Level NPC Converter (IJSRD/Vol. 2/Issue 07/2014/021)

Fig. 20: phase voltage waveform

Fig. 24: wind and Load active& reactive power with 9 level

Fig. 21: line voltage of eleven level inverter

Fig. 25: wind and Load active& reactive power with 11 level

Fig. 22: line voltage of eleven level inverter

Active and reactive power is controlled dc stabilization and the reactive power is near to unity Here PI controller is used to control the inverter output rms voltage and LC filter is used to remove the harmonics available in the system.

As the wind speed varies the voltage and current also varies these affects the grid power as speed are going to decreasing the active and reactive power also decreasing the pitch angle controller is used to control the blade angle at đ?œƒ = 0. The MPPT is used to track the maximum power From the above we can conclude that as the level of inverterIncreases line and phase voltage waveform increase and the harmonic induced is decreases. Using eleven levels neutral point clamped converter and nine levels NPC the harmonics reduces significantly. This is the advantage of multilevel inverter. From the FFT analysis of nine level NPC inverter and eleven level NPC inverter the THD of nine level is 12.87% which has more than eleven level NPC inverter is 7.46% i.e. as the level of inverter increases THD decreases.

IV. CONCLUSION

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Fig. 23: FFT Analysis for eleven level inverter

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Grid‐ Connection Control and Simulation of PMSG Wind Power System Based on Multi ‐ Level NPC Converter (IJSRD/Vol. 2/Issue 07/2014/021)

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