grid connection control and simulation of pmsg wind power ... · multilevel inverter is best suited...

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

All rights reserved by www.ijsrd.com 83

Grid‐Connection Control and Simulation of PMSG Wind Power System

Based on Multi‐Level NPC Converter Sandeep Kumar Gautam1 K P Singh2

1M.Tech Student 2Associate Professor 1,2Department 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

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).

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

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:

𝑃𝑎𝑏𝑐 = 𝑣𝑎𝑠𝑖𝑎𝑠 + 𝑣𝑏𝑠𝑖𝑏𝑠 + 𝑣𝑐𝑠𝑖𝑐𝑠 (1)

or in the dq-axes reference frame as follows:

𝑃𝑑𝑞 =3

2(𝑣𝑑𝑠𝑖𝑑𝑠 + 𝑣𝑞𝑠𝑖𝑞𝑠) (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:

𝑃𝑒𝑚 =3

2(𝑒𝑑𝑖𝑑𝑠 + 𝑒𝑞𝑖𝑞𝑠) (3)

Where 𝑒𝑞 = 𝑤𝑒𝐿𝑑𝑖𝑑𝑠 + 𝑤𝑒∅𝑟 = 𝑤𝑒∅𝑑 (4)

𝑒𝑑 = −𝑤𝑒𝐿𝑞𝑖𝑞𝑠 = −𝑤𝑒∅𝑞 (5)

Here,𝑒𝑑 and 𝑒𝑞 , are the back EMFs in the dq-axes

reference frame, and ∅𝑑 and ∅𝑞 are the dq-axes flux

linkages. Substituting expressions (4) and (5) into (3), the

active power can be re-expressed as follows:

𝑃𝑒𝑚 =3

2𝑤𝑒(∅𝑑𝑖𝑞𝑠 − ∅𝑞𝑖𝑑𝑠) (5)

Hence, the electromagnetic torque developed by a PMSM

can be deduced as follows:

𝑇𝑒 =𝑃𝑒𝑚𝑤𝑒𝑝2

=3

2(

𝑝

2) (∅𝑑𝑖𝑞𝑠 − ∅𝑞𝑖𝑑𝑠) (6)

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

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]:-

𝑉𝑎𝑜 = 𝑉𝑎1 + 𝑉𝑎2 +V𝑎3+V𝑎4+… (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

𝑓(𝑥) = 𝑎0 + ∑ (𝑎𝑛 cos𝑛𝜋𝑥

𝐿+ 𝑏𝑛 sin

𝑛𝜋𝑥

𝐿)

∞

𝑛=1… (8)

in term of Bn the equation can be written as:

𝐵𝑛 = (4𝑉𝑑𝑐

𝑛𝜋) ∑ 𝐶𝑂𝑆(𝑛𝛼𝜅)∞

𝑗=1 … (9)

j = no. Of dc source

n= no of odd harmonics

𝛼𝜅 = switching angle of level k

By solving above equation (3)

cos 𝛼1 + cos 𝛼2 + ⋯ … … . cos 𝛼𝑘 =𝑗𝑀

4

cos 3𝛼1 + cos 3𝛼2 + ⋯ + cos 3𝛼𝐾 = 0

cos 5𝛼1 + cos 5𝛼2 + ⋯ + cos 5𝛼𝐾 = 0

The above equation can be solved by using Newton

Raphsonmethod to find switching angle.

Fig. 2: Simulink model of full circuit

A. Simulink Model of Wecs

Fig. 3: Simulink model of wind energy conversion system

Fig. 4: Simulink model of wind turbine

Fig. 5: wind speed at 12 m/sec

Fig. 6: waveform of wind turbine at 12 m/sec wind speed




Fig. 7: Stator current of PMSG

Fig. 8: Simulink model of generator terminal

Fig. 9: Dc link Voltage

Fig. 10: Simulink model of nine level inverter

B. Simulation Results Of Nine Level Inverter

Fig. 12: phase voltage waveform of nine level inverter




Fig. 14: phase voltage waveform

Fig. 15: line voltage of nine level inverter

Fig. 16: line voltage waveform

Fig. 17: FFT analysis of nine level inverter

Fig. 18: Simulink model of eleven level inverter

C. Simulation Result Of Eleven Level Inverter






Fig. 21: line voltage of eleven level inverter

Fig. 22: line voltage of eleven level inverter

Fig. 23: FFT Analysis for eleven level inverter

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

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

level

IV. CONCLUSION

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

𝜃 = 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.

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grid connection control and simulation of pmsg wind power ... · multilevel inverter is best suited...

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