DSTATCOM BASED VOLTAGE SAG MITIGATION AND HARMONICS SUPPRESSION USING SYNCHRONOUS REFERENCE FRAME THEORY

LITERATURE SURVEY

Tejas Zaveri, et.al (2011), described a novel approach based on an improved

instantaneous active and reactive current component theory for generating reference currents for

distribution static compensator (DSTATCOM). An improved instantaneous active and reactive

current component theory, the compensating currents are obtained from the instantaneous active

and reactive current components of the load. Load currents in stationary reference frame are

obtained by applying Clarke’s transformation. Load currents in rotating (dq) reference frame are

obtained by applying Park’s transformation. Linear unbalanced load is realized by star connected

resistive–inductive load whereas non-linear load is simulated by three-phase rectifier with RLC

load. The proposed scheme is capable to achieve power factor correction, balancing of source

currents and reduction in source VA rating compared to uncompensated case, effectively, under

various source conditions. Simulation results indicate that the proposed technique is accurate and

robust for a wide variation in source and load conditions.

Bhim Singh, et.al (2011), described a new control approach for capacitor supported

DSTATCOM in three-phase four wire distribution system under non-ideal supply voltage

conditions based on synchronous reference frame theory. a control approach based on

synchronous reference frame (SRF) theory is used under non-sinusoidal supply conditions for the

three phase four-leg VSC based DSTATCOM system. The DSTATCOM consists of a 4-leg

pulse width modulated (PWM) voltage– source converter using eight insulated-gate bipolar

transistors (IGBTs), four interface inductors, and a DC capacitor. Performance of DSTATCOM

with non-linear load for harmonic compensation, load balancing and UPF operation. The control

approach has compensated the neutral and harmonic currents, reactive power, terminal voltage as

well as unbalanced load and the linear load for neutral current compensation, load balancing and

ZVR operation. DSTATCOM is almost maintained to the reference value under all disturbances.

Tejas Zaveri, et.al (2012), described a Distribution static compensator (DSTATCOM)

for balancing of source currents, power factor correction and harmonic mitigation in three-phase,

three-wire distribution system supplying delta connected load under various source voltage

conditions. DSTATCOM has been used extensively for reactive power compensation,

balancing of source currents and harmonic compensation in the distribution system. Improved

instantaneous active and reactive current component method has used. . An improved

instantaneous active and reactive current component theory, the compensating currents are

obtained from the instantaneous active and reactive current components of the load. Load

currents in stationary reference frame are obtained by applying Clarke’s transformation. Load

currents in rotating (dq) reference frame are obtained by applying Park’s transformation.Control

algorithm is validated using MATLAB/SIMPOWER software. Linear load is realized by

resistive-inductive load whereas non-linear load is simulated by three-phase rectifier with RLC

load.

It has been observed from simulation results that the uncompensated source current and

the source voltage of the respective phase are not in alignment for linear as well as non-linear

load under various source voltage conditions. Therefore, source has to supply reactive power if

compensator is not available. Further, uncompensated source currents are unbalanced. In

addition, source currents without compensation are highly distorted in case of non-linear

unbalanced load. The proposed scheme is capable to restrict THD of source current within IEEE-

519 standard harmonic current limits under any condition of use.

An Luo, et.al (2011), described the negative sequence equivalent circuit of DSTATCOM

in unbalanced distribution networks. A new control model of negative sequence voltage without

current sensors based on instantaneous power balancing algorithm is deduced. To compensate

for balanced and unbalanced voltages, a new cascade voltage loop control strategy, the negative

sequence voltage control loop is parallel to the positive sequence voltage loop, is used

The DSTATCOM output voltage command is directly obtained from the bus voltage at

the Point of Common Coupling (PCC) and the DC-side voltage via a simple algebraic algorithm

based on power balance equation. In addition, the implementation costs can be reduced since

current sensors are not required. DSTATCOM device is used to regulate and balance voltage in

the distribution network, which is based on a PWM controlled voltage source converter (VSC)

and connected to the distribution network through a LC filter. The results demonstrate good

performance in balancing the voltage along with enhancing the power factor.

Georgios Karmiris, et.al (2012), described a novel control scheme for a distribution

static compensator (DSTATCOM) aimed at mitigating voltage sag at the Point of Common

Coupling (PCC). A d–q reference frame for the decoupling of active and reactive current

components has used to derive the reference signal for produce a switching pulse for

STATCOM. To achieve multifunction operation of the DSTATCOM, a selection algorithm has

used. The first one is called ‘‘voltage sag mitigation’’. This function generates the appropriate

reference signals in such a way that the DSTATCOM injects reactive current at the PCC. The

second function is called ‘‘current harmonics elimination’’. This function creates reference

current which contains the harmonic components of the load current. The DSTATCOM

controller is based on a three phase three level VSI with flying capacitors.

The control algorithm chooses current harmonics elimination control when the amplitude

of the voltage at PCC is close to unity (Vs > 0.98 pu), while in case of the voltage drop i.e. (Vs =

0.98 pu) the voltage sag mitigation control is selected. The switching pattern generation which

has been chosen to generate the switching pulses is the sinusoidal pulse width modulation

(SPWM) technique. The output of the SPWM triggers the IGBTs of the multilevel inverter. From

this study the selection algorithm more suitable for both harmonics elimination and voltage sag

mitigation.

An Luo, et.al (2009), described a combined system of static VAR compensator (SVC)

and active power filter (APF) was proposed. The system has the function of power factor

correction, voltage stability, and harmonic suppression. The SVC, which consists of delta-

connected thyristor controlled reactor (TCR) and Y connected passive power filter (PPF), is

mainly for voltage stability and power factor correction. APF is used to filter harmonics

generated by the nonlinear load and the TCR in the SVC and to suppress possible resonance

between the grid and the PPFs. An optimal nonlinear proportional integral control was proposed

to improve the dynamic response and decrease the steady-state error of the SVC. This method

can eliminate harmonics generated by nonlinear loads and the TCR and compensate reactive

power dynamically, as well as suppress the possibility of resonance between the SVC and the

grid.

Bhim Singh, et.al (2010), described a simple electricity generating system for supply

electricity in remote areas. Here extraction of the petroleum products under the sea was

discussed. A major drawback of SEIG is its poor voltage regulation, as the voltage drops

considerably with load in the absence of a regulator. This problem was deal with STATic

COMpensator (STATCOM). The STATCOM consists of a three phase insulated-gate bipolar-

transistor (IGBT)-based current controlled voltage-source inverter (CC-VSI), DC bus capacitor,

and AC inductors. The SEIG–STATCOM system with static and dynamic loads is simulated

under various loading conditions. The STATCOM has the advantages of harmonic-free

sinusoidal voltage and maintain constant voltage at the terminals of SEIG, and, hence, the

consumer gets good quality supply.

Kenichiro Sano, et.al (2012), described a cascaded multilevel converter which has

multiple DC voltage values for a 6.6-kV transformerless distribution static synchronous

compensator (D-STATCOM). The existing D-STATCOM is equipped with a step-down

transformer and an AC filter. In this case, the transformer and the filter inductors make the

STATCOM bulky and heavy. In this purpose Cascaded multilevel converters have been studied

to realize a small and lightweight STATCOM.A three-phase downscaled STATCOM rated at

220 V and 10 kVA was built and tested. Si-MOSFETs (rated at 250 V for HV cells, 100 V for

MV cells, and 60 V for LV cells) were applied to the circuit instead of insulated gate bipolar

transistors (IGBTs). A downscaled experimental model rated at 220 V and 10 kVA was built and

tested. The experimental results proved the stable operation in the startup, steady state, and

output power change. Fundamental fault ride through capability was also verified by the

experiments.

P. Salmerón, et.al (2010), described control algorithm for a three-phase hybrid power

filter. Here a series active filter and a passive filter connected in parallel with the load. The

control strategy is based on the vectorial theory dual formulation of instantaneous reactive

power, so that the voltage waveform injected by the active filter is able to compensate the

reactive power and the load current harmonics and to balance asymmetrical loads. the proposed

control algorithm, the active filter improves the harmonic compensation features of the passive

filter improve the power factor of the load. Simulations with the MATLAB-Simulink platform

were performed with different loads and with variation in the source impedance.

Gaurav Kumar Kasal, et.al (2008), described decoupled voltage and frequency

controller (DVFC) for an isolated asynchronous generator (IAG) to control the voltage and

frequeny at generator terminal independently. Here STATCOM and electronic load controller

(ELC) are used to control the voltage and frequency. This controller functions in

decoupled manner to regulate the voltage and frequency. For regulating the voltage, it controls

the reactive power while the frequency is controlled through active power control and it

functions as a decoupled voltage and frequency controller (DVFC). The DVFC is a combination

of a STATCOM and an ELC. The STATCOM is functioning as a voltage regulator, a neutral

current compensator, and a load balancer and the ELC is used to maintain the constant power at

generator terminals, which regulates the frequency of the system. The generated voltage and

frequency are not affected and remain constant during the changes in consumer loads due to

STATCOM. This method was reduced excitation capacitor size and also suitable for the voltage

and frequency control along with load balancing, neutral current compensation.

From the literature survey various methods are discussed for power quality improvement

in distribution system. Active power filter and passive power filter having limitation on size,

cost, mistuning, instability and difficulty to use in high voltage grid. This problems are overcome

by STATCOM with the help of higher rating component innovate in power electronics

industries. In this project deals the power quality problems with the help of DSTATCOM.