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2/10/2016 Modeling and Simulation of DSTATCOM for Voltage Regulation Imparting Various Control Strategies | Dhananjay Mishra Academia.edu
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Modeling and Simulation of DSTATCOM for Voltage
Regulation Imparting VariousControl Strategies
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National conference on Trends & Challenges in Applied Science and Engineering
21-22 Jan 2014 SATI Vidisha (M.P)
Abstract — This paper describes the modeling, controlling and
simulation of Distributed static synchronous compensator
(DSTATCOM). It is important for a distribution system to have
controllability, voltage stability and good power transfer
capability. Here, voltage source converter based d-statcom
achieves voltage regulation in the system by absorbing or
supplying the required reactive power. The system is modeled
using various control strategies like direct and indirect control
which includes D-Q transform. The comparative analysis of the
control strategies has been done. The results of simulation are
demonstrated and analyzed using MATLAB.
I ndex Terms — reactive power compensation, DSTATCOM,
dq-model, phase shift, voltage control, VSC.
I. INTRODUCTION
He rapidly developing power electronics technology providesan opportunity for developing new power equipment for
improving the performance of the power system. Flexible AC
Transmission system technology (FACTS) uses the latest powerelectronic devices and methods to control electronically the high-voltage side of the network. FACTS devices can be used for
power flow control, voltage regulation, transient stability
improvement, and damping of power oscillations. FACTS devicescan be of shunt or series or combination of shunt and series types.The shunt devices can be used for voltage regulations, while seriesdevices can be used for regulation of line impedance and series -
parallel combination can be used for real and reactive powercompensation in addition to regulation of voltage and regulation ofline impedance [1]
The f a m i l y of e m e r g i n g power electronic devices
being offered to achieve these custom power objectives is: (i)
Distribution Static Compensator (DSTATCOM) that protects the
distribution system from the effects of fluctuating voltage, voltage
sags and swells and non-linear loads, (ii) DVR that protects a
critical load from disturbances like sags, swells, transients and
harmonics originating on the interconnected distribution system,
(iii) Unified Power Quality Conditioner (UPQC), a combination of
series and shunt controller, which compensates supply voltage
and load current imperfections in the distribution system.
The DSTATCOM is a versatile device for providing reactive
power compensation in ac networks. The control of reactive
power is achieved via the regulation of a controlled voltage
source behind the leakage impedance of a transformer [2]. It is
similar to a conventional synchronous compensator, which is
essentially a synchronous generator where the field current is used
to adjust the regulated voltage. The DSTATCOM uses voltage
source converter (VSC) to achieve the regulation task. When used in
low or medium voltage distribution systems the STATCOM is
normally identified as Distribution STATCOM (D-STATCOM). It
operates in a similar manner as t h e STATCOM (FACTS
controller), with the active power flow controlled by the angle
between the AC system and VSC voltages and the reactive
flow controlled by the difference between the magnitudes of these
voltages. As with the STATCOM, the capacitor acts as the energy
storage device and its size is chosen based on power ratings, control
and harmonics considerations. The D-STATCOM controller
continuously monitors the load voltages and currents
determines the amount of compensation required by the AC system
for a variety of disturbances.
The DSTATCOM is a shunt device. It should therefore be ableto regulate the voltage of a bus to which it is connected. The operating
principle of a DSTATCOM in this mode has been termed DSTATCOM in voltage control mode. This report shows that even
though the structure of DSTATCOM used in both current control andvoltage control modes is the same, its operating principle is different.In the current control mode it is required to follow a set of reference
currents while in the voltage control mode it is required set of reference voltages. This paper discusses the reference voltage
generation scheme and the control of DSTATCOM in the voltagecontrol mode.
II. BASIC CONFIGURATION OF D-STATCOM
The D-STATCOM system comprises of a VSC, a set of
coupling reactors (leakage reactances of the transformer) and a
controller. The D-STATCOM generates a controllable ac voltage
from the voltage source inverter (VSI) connected to a dc capacitor
(energy storage device). The ac voltage appears behind the
transformer leakage reactance.
Fig.1 Basic Block Diagram of D-STATCOM
The active and reactive power transfer between the power system
and the D-STATCOM is caused by the voltage difference across
this reactance. The D-STATCOM is connected to the power network
at the point of common coupling (PCC), where the voltage-quality
problem is a concern. All required voltages and currents
measured and are fed into the controller to be compared with the
reference. The controller then performs feedback control and
Modeling and Simulation of D-STATCOM for Voltage
Regulation Imparting Various Control Strategies
Dhananjay Kumar, Nupur Jejurikar and Pradyumn Chaturvedi
Electrical Engineering Department, SATI, Vidisha (MP), India-464001
[email protected], [email protected] , [email protected]
T
National conference on Trends & Challenges in Applied Science and Engineering
outputs a set of switching signals to drive the main semiconductor
switches (IGBTs) of the power converter accordingly [3]. The basic
IV. MODELING OF DSTATCOM
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21-22 Jan 2014 SATI Vidisha (M.P)
switches (IGBTs) of the power converter accordingly [3]. The basic
diagram of the D-STATCOM is illustrated in figure 1.
III. PRINCIPLE OF DSTATCOM
D-STATCOM is to suppress voltage variation and control reactive
power in phase with system voltage. It can compensate for inductive
and capacitive currents linearly and continuously. Figure 2 shows
the vector diagram at the fundamental frequency for capacitive and
inductive modes and for the transition states from capacitive to
inductive and vice versa. The terminal voltage () is equal to the
sum of the inverter voltage () and the voltage across the
coupling transformer reactive VL in both capacitive and
inductive modes. I mean that if output voltage of
DSTATCOM () is in phase with bus terminal voltage () and
() is greater than D-STATCOM provides reactive power to
system.And if is smaller than , D-STATCOM absorbs reactive
power from power system. and have the same phase, butactually they have a little phase difference to component the loss oftransformer winding and inverter switching, so absorbs some real
power from system.
Figure 2 is DSTATCOM vector diagrams, which show inverteroutput voltage VI, system voltage VT, reactive voltage VL and line
current I in correlation with magnitude and phase δ. Figure 2.a and bexplain how VI and VT produce capacitive or inductive power bycontrolling the magnitude for inverter output voltage VI in phase with
each other.
Figure 2: Vector diagram of DSTATCOM(a) Capacitive mode, (b) inductive mode
Fig.3 Simplified single line diagram of D-STATCOM
Rf ia + Lf dia/dt = Vsa-Vca (1)
Rf ib + Lf dib/dt = Vsb – Vcb (2)
Rf ic + Lf dic/dt = Vsc – Vcc (3)
Here,Vsa, Vsb, Vsc : Voltage at the PCCVca, Vcb ,Vcc : Inverter output voltage
Lf : Filter inductanceRf : Equivalent filter resistanceC : DC Link capacitor
*Designing a) Qstat= √3 V Ic
b) Vdc= 2√2 V /√3mac) Lac= (√3ma Vdc)/ 12a fs I(statp-p)
d) Capacitor designingCdc= 3Vs ΔIL T/(Vdc^2 – Vdc1^2)
Here,Ic =dstatcom line current
V= line voltageMa= modulation indexVdc = dc link voltageQstat= power rating
V= line voltageLac = ac inductor
a= over current factor (1.2)
*Park’s transformation:-
This block performs the abc to dq0 transformation on a set of three-
phase signals. It computes the direct axis Vd, quadratic axis zero sequence V0 quantities in a two axis rotating reference frameaccording to the following transformation:The following transformation is used:
Vd=2/3*[Va*sin(wt)+Vb*sin(wt-2pi/3)+ Vc*sin(wt+2pi/3)]Vq=2/3*[Va*cos(wt)+Vb*cos(wt-2pi/3)+Vc*cos(wt+2pi/3)]V0 = 1/3*[Va + Vb + Vc]
Where w= rotation speed (rad/s) of the rotating frame.
This transforms three quantities (direct axis, quadature axis and zero-sequence components) expressed in a two axis reference frame back
phase quantities.
National conference on Trends & Challenges in Applied Science and Engineering
The following transformation is used:
Va = [Vd*sin(wt) + Vq*cos(wt) + Vo ]
Vb = [Vd*sin(wt-2pi/3) + Vq*cos(wt-2pi/3) + Vo)Vc = [Vd*sin(wt+2pi/3) + Vq*cos(wt+2pi/3) + Vo)where w= rotation speed (rad/s) of the rotating frame.
V. CONTROL STRATEGIES
Satisfactory performance, fast response, flexible and easy
implementation are the main objectives of any compensationStrategy .the control strategy of DSTATCOM are mainly implementedin the following steps[4],[5]:*Measurements of system variables and signal conditioning.*Extraction of reference compensating signals.
*Generation of firing angles for switching devices.
Phase shift control
In this control algorithm the voltage regulation is achieved in a D-STATCOM by the measurement of the rms voltage at the load
point and no reactive power measurements are required. Fig.4shows the block diagram of the implemented scheme (4)
Since vq=0, id and iq completely describe the instantaneous value ofreal and reactive powers produced by the DSTATCOM when thesystem voltage remains constant. Therefore the instantaneous three
phase current measured is transformed by abc to dqo transformation.The decoupled d- axis component id and q axis component iq areregulated by two separate PI regulators. The instantaneous idreference and the instantaneous iq reference are obtained by thecontrol of the dc voltage and the ac terminal voltage measured.Thus, instantaneous current tracking control is achieved using foPI regulators. A Phase Locked Loop (PLL) is used to the control loop to the ac supply so as to operate in the adqo reference frame.
2/10/2016 Modeling and Simulation of DSTATCOM for Voltage Regulation Imparting Various Control Strategies | Dhananjay Mishra Academia.edu
http://www.academia.edu/8538560/Modeling_and_Simulation_of_DSTATCOM_for_Voltage_Regulation_Imparting_Various_Control_Strategies 3/5
21-22 Jan 2014 SATI Vidisha (M.P)
shows the block diagram of the implemented scheme (4)
Fig.4. Block diagram of phase shift control
Sinusoidal PWM technique is used which is simple andgives a good response. The error signal obtained by comparing themeasured system rms voltage and the reference voltage, is fed to a
PI controller which generates the angle which decides thenecessary phase shift between the output voltage of the VSC and theAC terminal voltage. This angle is summed with the phase angle ofthe balanced supply voltages, assumed to be equally spaced at 120
degrees, to produce the desired synchronizing signal requiredto operate the PWM generator. In this algorithm the D.C. voltage ismaintained constant using a separate dc source.
Decoupled current control p-q theory
This algorithm requires the measurement of instantaneous
values of three phase voltage and current. Fig.5. shows the blockdiagram representation of the control scheme. The compensation isachieved by the control of id and iq. Using the definition of theinstantaneous reactive power theory for a balanced three phase three
wire system, the quadrature component of the voltage is always zero,the real (p) and the reactive power (q) injected into the system bythe DSTATCOM can be expressed under the dq referenceframe as:
P = Vd Id + Vq Iqq = Vq Id - Vd Iq
Fig.5. block diagram of decoupled theory based control ofD-STATCOM
VI. SIMULATION RESULTS
In this work, the performance of VSC based power devices
acting as a voltage controller is investigated.
Phase shift control
It does not have a self supporting dc bus and requires aseparate dc source to pre-charge the dc side capacitor & maintain
its voltage during the operation of D-STATCOM .It assumes the supply side voltage is balanced and without harmonics, sincefundamental wave form is used to obtain the phase angles supply wave form. There is no provision for harmonic suppression
in case the load connected to PCC is nonlinear. This method results
in generation of active power by the VSC along with the var.
Fig.6. Simulink model for phase shift control
National conference on Trends & Challenges in Applied Science and Engineering
.
Source voltage
DC voltage
Inverter voltage
Compensated output voltage and current
Fig.6 Simulink model for decoupled current control
Source voltage
Load current
0 1000 2000 3000 4000 5000 6000 7000 8000 9000-400
-300
-200
-100
0
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TIME(SEC)
s o u r c e v o l t a g e
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000
100
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D C v o l t a g e
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000-800
-600
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l o a d v o l t a g e ,
l o a d c u r r e n t
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v o l t a g e ( v )
Modeling and Simulation of DSTATCOM for Voltage Regulation Imparting Various Contro… DOWNLOAD
2/10/2016 Modeling and Simulation of DSTATCOM for Voltage Regulation Imparting Various Control Strategies | Dhananjay Mishra Academia.edu
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21-22 Jan 2014 SATI Vidisha (M.P)
Decoupled current control
The advantageous features of this scheme are:
It incorporates a self supporting dc bus. The active and reactive power control achieved through id and iq control are decoupled from
each other. The dc bus control/ regulation are decoupled from the
ac bus control like voltage regulation or power factor correctionand load balancing.
Switching of devices of VSC is done at fixed frequency. Thus
switching losses can be limited within the rating of the devices.
This type of control is inherently linear & robust and uses PI or
PID controls.
DC voltage
SPWM technique
0 5000 10000 0
100
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time(sec)
5000 5020 5040 5060 5080 5100 5120 -3
-2
-1
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time(sec)
v o l t a g e
National conference on Trends & Challenges in Applied Science and Engineering
VII. CONCLUSION
Detailed modeling is presented and results are discussed withdifferent control studies. These Power devices provide solutions
to power quality at the medium and low voltage distributionnetwork level. This project presents the detailed modeling of one ofthe custom power products, DSTATCOM is presented usinginstantaneous P-Q theory and phase shift theory used for the
control of DSTATCOM are discussed. These control algorithmsare described with the help of simulation results under linear loadsand nonlinear loads. It was observed that undersized capacitordegrades all three aspects. On the other hand, an oversizedcapacitor may also lead to a PWM control with a sluggish
response but it will reduce D- STATCOM harmonic generationand transient overshooting. It is concluded that a DSTATCOMthough is conceptually similar to a STATCOM at the transmissionlevel; its control scheme should be such that in addition to complete
reactive power compensation, power factor correction and voltageregulation the harmonics are also checked, and for achievingimproved power quality levels at the distribution end.
S.no.
PARAMETERS
PHASE
SHIFT
CONTROL
DECOUPLED
CURRENT
CONTROL
1. Reactive powercompensation
Average Partial
2. Performance undernonlinear loads
Containsundesiredharmonics
Not Satisfactory
3. Applicable for single phase systems
Yes No
4. Harmonic
compensation
less average
5. PWM switchingfrequency
fixed Fixed
6. Self supporting DC bus
No Yes
7. Generation of firing
pulses
Sine PWM Sine PWM
8. Power factor .8 to.97(linear)
.8 to .94(linear)
.8 to
.92(nonlinear)
.8 to
.95(nonlinear)
9. Response time less More
10. Control scheme easy complex
VIII. FUTURE WORK
This project presents a detailed modeling and analysis ofone of the custom power device DSTATCOM.Instantaneous Decoupled Current Control or instantaneous
p-q theory and phase shift control is discussed and verifiedthrough detailed simulations by developing the models inMATLAB simulink using the sim power system control tool
boxes. Now we are posing a challenge to complete If the
remaining control strategies which includes the synchronousframe theory, regulation of Bus and DC link voltage, andANN based Adaline theory .these control strategies are
implemented and studied in detail through varioussimulations then it would be of immense help for the realtime implementation of the DSTATCOM across all over the
globe. If thrown light on other custom power devices like the
Dynamic voltage Regulator (DVR), and Unified powerquality conditioner (UPQC), applying different strategies
then we can bring a revolution in the control of power in thedistribution systems.
REFERENCES
[1] N. Hingorani, “FACTS — Flexible ac transmission systems
IEE 5th Int. Conf. AC DC Transmission, London, U.K., 1991, Conf. Pub.
345, pp. 1 – 7.
[2] P. Lehn and M. Iravani, “Experimental evaluation of STATCOM
closed loop dynamics,” IEEE Trans. Power Delivery, vol. 13, pp.
1378 – 1384, Oct. 1998.
[3] “Introducing custom power,” IEEE Spectrum, vol. 32, pp. 41
1995.
[4] “Control Algorithms for Distribution Static Compensator
Masand, Shailendra Jain and Gayatri Agnihotri and Maulana AzRad
Dept. Of Electrical Engineering National Insti tute of Technology, Bho
(MP), India.
[5] “A comparative study of Control algorithms
DSTATCOM for load compensation” by Bhim Singh, Department
of Electrical Engineering, Indian Institute of Technology ,Hauz Khas ,
New Delhi .
[6] Pierre Giroux, Gilbert Sybille and Hoang Le-Huy,
and Simulation of a Distribution STATCOM using
Power System Block set,” IECON’01: the 27th Annual Conference of the
IEEE Industrial Electronics Society, 2001.
[7] D.Masand, S.Jain and G.Agnihotri, “Distribution Static
Compensator Performance under Linear and Nonlinear Current
Regulation Methods” J. Electrical System 4-1 (2008): pp.91-105.
2/10/2016 Modeling and Simulation of DSTATCOM for Voltage Regulation Imparting Various Control Strategies | Dhananjay Mishra Academia.edu
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