Transcript
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Using 11-level VSC based STATCOM
FLICKER MITIGATION IN VOLTAGE
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FLICKER IN VOLTAGE ?
Flicker is rapid visible changes of light level. Definition of thecharacteristics of voltage fluctuations that produce objectionable lightflicker has been the subject of ongoing research.
Flicker is addressed as random or repetitive variations in the RMS voltagebetween 90 and 110% of nominal.
This phenomenon is always caused by arc furnaces.
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NEED FOR FLICKER MITIGATION
The voltage current characteristic of the arc is nonlinear, and is the causeof harmonic currents.
These harmonic currents, when circulated in the electric network cangenerate harmonic voltages which in turn can affect other users.
Blinking in incandesant bulbs is observable under voltage flicker inhousehold.
Flicker may also affect sensitive electronic equipment such as televisionreceivers or industrial processes relying on constant electrical power.
Lifetime of electrical appliances decrease.
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FLICKER COMPENSATION TECHNIQUES
The most commonly used methods for compensation of voltage flicker isby regulating the EAF passive components, static VAR compensator (SVC)and DSTATCOM.
Distribution Static Compensator (DSTATCOM), which consists of an GTO-based voltage source converter, uses advanced power switches to provide
fast response and flexible voltage control at the PCC for power qualityimprovement in distribution systems.
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STATCOM ?
The STATCOM has been defined as per CIGRE/IEEE with following threeoperating structural components. First component is
Static: based on solid state switching devices with no rotatingcomponents; second component is
Synchronous: analogous to an ideal synchronous machine with 3sinusoidal phase voltages at fundamental frequency; third component is
Compensator: provided with reactive compensation
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TYPES OF STATCOMS
STATCOM is one of the key Converter-based Compensators which areusually based on the VSI or CSI.
VSC are often preferred over current sourced converters for FACTSapplications.
The STATCOM is composed of a VSC with a dc capacitor, couplingtransformer, and signal generator and control circuit .
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Principle of operation
The STATCOM is basically a DC-ACvoltage source converter with anenergy storage unit, usually a DCcapacitor.
It operates as a controlled SVSconnected to the line through acoupling transformer. Fig. shows the
schematic configuration ofSTATCOM.
The STATCOM regulates voltage atits terminals by controlling theamount of reactive Current injectedinto or absorbed from the powersystem.
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V-I & V-Q CHARACTERISTICS OF STATCOM
The STATCOM is essentially an alternating voltage source behind a couplingreactance with the corresponding V-I and V-Q characteristics shown in figbelow.
These show that STATCOM can be operated over its full output current rangeeven at very low (theoretically zero), typically about 0.2 p.u. system voltage
levels.
V-I characteristics V-q characteristics
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ADVANTAGES OF STATCOM
Quicker response time (A STATCOM has a step response of 8 ms to 30ms). Thishelps with compensation of negative phase current and with the reduction ofvoltage flicker.
Active power control is possible with a STATCOM (with optional energy storageon dc circuit). This could further help with system stability control
High efficiency
High dynamic and very fast response time
Single phase control for unbalanced
Enables grid code compliance
Small footprint
Maximum reactive current over extended
Enhanced ride-through capability voltage range
High reliability and availability
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APPLICATIONS OF STATCOM
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H-BRIDGE VSC
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CONTROL MECHANISMS OF STATCOM
types
closed loopcontrol
Fuzzy logiccontrol P-I control
open loopcontrol
D-q theory
P-Q theory
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OPEN LOOP CONTROL
The schematic diagram for open loop control of STATCOM is shown in figbelow
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CLOSED LOOP P-I CONTROL OF STATCOM
Closed loop d-q theory p-I control of STATCOM is as shown below.
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SIMULATION S IN MATLAB
Open loop control schema :-
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Output wave forms
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Closed loop control schema :-
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STATCOM CONTROLLER BLOCK
Statcom ocntroller block consists of the following blocks
1.) PLL block with abc/dqo converter
2.) Ac voltage regulator
3.) Current regulator
4.) steady state MI regulator & Transcient MI regulator
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SIMULATION RESULTS OF CLOSED LOOP
CONTROL
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