Modelling and Simulation of DSTATCOM for Power

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Abstract-This paper presents Distribution Static Compensator. (DSTATCOM) modeled in the MATLAB SIMULINK toolbox for the mitigation of the power quality ...
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2015 International Conference on Energy Systems and Applications (ICESA 2015) Dr. D. Y. Patil Institute of Engineering and Technology, Pune, India 30 Oct - 01 Nov, 2015

Modelling and Simulation of DSTATCOM for Power Quality Improvement in Distribution System Using MATLAB Simulink Tool Mr.Sharad S.Pawar

Mr.A.P.Deshpande

Mrs.Meera Murali

Electrical Engineering Department College of Engineering, Pune. Maharashtra, India [email protected]

Electrical Engineering Department College of Engineering, Pune. Maharashtra, India [email protected]

Electrical Engineering Department College of Engineering, Pune. Maharashtra, India [email protected]

these techniques most commonly used the theories are synchronous reference frame (SRF) theory and instantaneous reactive power (IRP) theory[3].In this paper MATALAB based simulation of the DSTATCOM is carried out using instantaneous reactive power (IRP) theory for compensation of the reactive power, unbalance, reducing total harmonic distortion (T.H.D) and improving power factor of the system.

Abstract-This paper presents Distribution Static Compensator (DSTATCOM) modeled in the MATLAB SIMULINK toolbox for the mitigation of the power quality issues in the distribution system. DSTATCOM is one of the custom power device used in distribution system for power conditioning. DSTATCOM is developed for the compensating reactive power demanded by non-linear and unbalanced load. Also power factor of the source is improved and the Total Harmonic Distortion in the source currents is reduced. DSTATCOM can correct voltage sag, swell, unbalance by injecting the reactive current into the system. Instantaneous reactive power theory is used for obtaining reference source current for controlling DSTATCOM. The performance of the DSTATCOM by using the IRP theory for unbalanced and non linear load is demonstrated with the MATLAB simulation results.

II. SYSTEM CONFIGURATION A distribution feeder connected to unbalanced and non linear load is shown in the below Fig. 1. Working performance of the DSTATCOM using instantaneous reactive power theory (IRP) is analyzed by the modeling system shown in Fig.1 in MATLAB Simulink tool.

Keywords—Distribution Static Compensator (DSTATCOM); Instantaneous Reactive Power (IRP) Theory; Total Harmonic Distortion (T.H.D).

Vs

Vpcc

Is Rs

Ls

IL

I. INTRODUCTION

978-1-4673-6817-9/15/$31.00 ©2015 IEEE

Ic

DSTATCOM

Now-days most of the loads in industry, homes, agriculture are inductive in nature like induction motors, ceiling fan, agricultural pumps etc. In the case of these inductive loads currents drawn by the loads from source is lagging with respect to the voltage. So the reactive power burden on the system increases, which will increase losses in the distribution system and capacity of active power flow through the distribution system gets reduced. Due to advancement of power electronics technology, non linear loads in the system are increasing, such as rectifiers, inverters, uninterruptible power supply (UPS), computers, etc. These Non-linear loads can cause the production of frequency component of the currents in the system which are not fundamental frequency components. So due to such harmonic component of currents the quality of power gets affected[1]. Also, there is the impact of the unbalancing on transformers and generators operation. The solution to power quality improvement is the use of custom power device[2] like DSTATCOM. Control schemes reported in the literature for controlling of the DSTATCOM are synchronous reference frame (SRF) theory, current compensation using DC bus regulation, instantaneous reactive power(IRP) theory, a scheme based on the neural network technique. Out of all

Non-Linear And Unbalanced Load

Lf

Cdc

V.S.C Controller

Fig.1.Configuration of DSTATCOM

In the system diagram shown in above Fig. 1, Rs and Ls represents source resistance and source inductance. The nonlinear load is realized by connecting the three phase diode rectifier to a Resistive-Inductive load (R-L). Unbalanced load is realized by connecting different values of impedances in three phases. Three phase voltage source converter (VSC) act as the DSTATCOM which consist of the six insulated gate bipolar transistor (IGBT) and anti parallel diodes are connected to each IGBT[4]. DC side of the Voltage source converter (VSC) consists of a capacitor which is used to maintain constant voltage for the switching operation of the IGBT switches. The DC capacitor is not used for any reactive power compensation. Interfacing inductor, Lf is connected on

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the AC side of the voltage source converter for compensating high frequency components of the compensating currents [5]. Storage capacitor Cdc does not exchange any active power between DSTATCOM and the load. Breaker is used to observe the performance of the DSTATCOM before compensation and after compensation (i.e. For connecting and removing DSTATCOM to and from the system)

Similarly instantaneous active power in Į-ȕ frame can be written as

p

vD iD  vE iE

(4)

instantaneous reactive power can be written as,

q vE iD  vD iE

(5)

Above equations (4) and equation (5) can be written in matrix form as

III. CONTROL ALGORITHM The main function of DSTATCOM is to provide reactive power as demanded by the load. Therefore, with the help of DSTATCOM source currents are maintained at unity power factor and reactive power burden on the system gets reduced. Due to the compensation of the reactive power by DSTATCOM source has to supply only real power.

ª pº «q » ¬ ¼



ª vD « ¬« vE

vE º ªiD º »« » vD ¼» ¬iE ¼

ሺ͸ሻ

Reference source currents are to be calculated to compensate only instantaneous reactive power theory and some part of active power drawn from source to compensate for switching losses of IGBT devices during operation of VSC.DC link voltage controller play an vital role for maintaining constant dc link voltage.Sensed voltage of the dc link capacitor is compared with reference DC voltage and error is processed using PI controller.Output of PI controller is reference d axis component of current so it is added with active power LQVWDQWDQHRXV SRZHU IRU FDOFXODWLRQ RI UHIHUHQFH Į-ȕ component of source current from source instantaneous active and reactive power [3]. So reference source curreQWLQĮ-ȕIUDPHFDQEHZULWWHQDV,

Fig. 2. MATLAB Model of IRP Theory.

Theory of extracting reference currents using IRP was introduced by Akagi [6]. In this theory the three phase load currents are transformed into two phase Į-ȕ coordinate. The Į-ȕ co-ordinates are orthogonal to each other. According to the IRP theory the instantaneous real and reactive powers are calculated by using these Į-ȕ co-ordinates. Load voltages where load is being connected and load currents are used to generate the reference source currents. The reference currents obtained are then fed to the hysteresis based PWM controller to obtain the pulses to be fed to the IGBT switches of the DSTATCOM.Fig.2 is the MATLAB model of Instantaneous Reactive Power Theory (IRP) for controlling DSTATCOM.







ªiD º «i » ¬E¼

ª «1 « « «¬ 0

ª «1 « « «¬0



1 2 3 2



1 2 3 2

1 2 3  2 

1 ªvD « ' ¬«vE

 vE º ª p  Vd º ሺ͹ሻ » vD ¼» «¬ 0 »¼

where,

'

Transformation of the three phase currents and voltages into the two phase Į-ȕ IUDPH LV GRQH E\ XVLQJ WKH &ODUN¶V transformation as given below

ª vD º «v » ¬ E¼

ªiD* º « *» ¬«iE ¼»

º ªv º » « La » » « vLb » ሺͳሻ »« »¼ ¬ vLc »¼

vD2  vE2

ሺͺሻ

Finally reference source current in a-b-c frame can be estimatedwith the help of Reverse Clark’s transformation [7] given as, ª 1 º 1 0 « » * » ªi0* º ªisa º « 2 « «* »  1 1 3 » « * » ሺͻሻ  » «iD » «isb » « 2 2 »« *» «i * » « 2 iE ¬ sc ¼ « 1 1 3»¬ ¼ « »   2 2 ¼ ¬ 2 Zero sequence component of current is absent in case of three phase three wire system [3] so we can write

i0*

0 in above

equation (9)

1 º i ª La º 2 »« » » iLb ሺʹሻ 3»« » «i »  2 »¼ ¬ Lc ¼

IV. SIMULATION MODEL OF DSTATCOM



The basic DSTATCOM configuration connected to the radial distribution system at the point of common coupling as shown in Fig. 1 is modeled in MATLAB SIMULINK Block Set as shown in Fig. 3.Three phase source of having line to line voltage of 415 V is connected to the nonlinear and unbalanced load .In this case the non linear load considered is three phase diode rectifier connected to a combination of R-L load on the

Three phase instantaneous power in a-b-c axis can be written as p vLa iLa  vLb iLb  vLc iLc ሺ͵ሻ 

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DC side. Unbalanced load is realized using the different values of impedances for three phases.

factor of the source is not unity, as voltage at PCC and source currents are not in Phase with each other. Total Harmonic Distortion for the source current is 6.36% B. Results After Compensation

Fig. 3. MATLAB Model of DSTATCOM Using IRP Theory

DSTATCOM is realized with the help of three phase voltage source converter. On the DC side of VSC a storage capacitor Cdc of 5000uF is connected to maintain constant DC voltage of 700V by means of PI controller. The performance ofthe DSTATCOM using IRP theory is studied by simulating MATLAB model as shown in Fig. 3 by considering sample time equal to 10îíVHFDQGE\XVLQJWKH2GH 'RUPDQGPrince) solver.

Fig. 5. Simulation Results with DSTATCOM

After connecting DSTATCOM to the system it is observed from Fig.5 that load current is same which is drawn by load but source current is approximately sine wave, also source current and voltage at PCC are in phase with each other. So, power factor is maintained equal to unity. Total Harmonic Distortion (T.H.D) in the source current is found to be 0.43% which is very less compare to T.H.D before compensation.

V. SIMULATION RESULTS The performance of the DSTATCOM using IRP theory for power quality improvement in the distribution system is studied by observing waveforms of the different parameters of the system before compensation and after compensation. A. Results Before Compensation Fig. 4 shows the results of simulation without connecting the DSTATCOM to the Point of Common Coupling (PCC).

C. Compensator Current

Fig. 6. Compensator Current

From Fig. 6 it is clear that DSTATCOM is connected to the system at 0.4 second, so before connecting the DSTATCOM to system the current injected by DSTATCOM into system is zero but after connecting DSTATCOM it will inject reactive current into system to maintain the unity power factor and also to improve power quality of the system. Fig. 4. Simulation Results Without DSTATCOM

D. DC Link Voltage Fig. 7 shows that, DC link voltage of the DSTATCOM is maintained at constant level of 700V DC with the help of PI

From Fig. 4 it is observed that due to unbalanced and non linear load, source currents and load currents get unbalanced and some distortion is present in their waveform. Also power

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controller for the proper switching operation of the IGBT g source converter. device of voltage

response of the DSTATCOM is fast for compensation of the reactive power as compared to conventional reactive power control devices. REFERENCES [1] [2] [3]

[4] Fig. 7. DC Link Voltage [5]

VI. CONCLUSION

[6]

Custom power devices can be used for power quality improvement in the distribution system.IRP theory for controlling the DSTATCOM reduce the unbalance in the system, harmonic components are also reduced. Power factor of the system is improved and maintained equal to unity. The

[7]

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