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H64APCH64APC
FACTsFACTs and Distributedand Distributed
Power SystemsPower Systems
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STATCOMSTATCOM A PowerA Power
Electronic SystemElectronic System
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STATCOM
Power converter connected via a coupling
inductor to the power system
Behaves as a current controlled source
Injects current with leading or lagging
power factor onto the power system
If Vpcc (Voltage at point of common
coupling) remains reasonably constant,
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the STATCOM can be considered as asource of leading or lagging reactive
power
Has very fast current control loops andcan react quickly to maintain system voltage
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STATCOM
pwmV
dcV
ccV
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Controlled Current Source
Control Vpwm with respect to Vpcc to
control the current in the inductor
(and injected into the supply)
Identical structure to Sinusoidal (PWM)
Rectifier
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Principle of Operation
Istat controlled to lead Vpcc (phase) by 90o
Magnitude of Istat determined by
1. Specific reactive power demand from
system wide controller
2. Locally controlled to regulate Vpcc
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to control Vpcc
Consider behaviour of a simple system in the
presence of a load change
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Phasor Diagrams
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Control
Nested control system normally employed
Outer loop measures and controls Vpcc to
match a reference value Vpcc*
Outer loop provides reference for themagnitude of Istat
Inner loop provides fast control of the
current.
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Control Design
Assume ideal inner current loop
E.g. vector control or hysteresis control
Need model of the system to design outer
voltage controller
Consider steady state
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Control Design
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Controlled Voltage Source
pwmV
dcV
ccV
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Voltage Source Inverter (VSI)
Converts DC to AC (for simplicity assume
Vdc is an ideal voltage source
Uses pulsewidth modulation (PWM)
Vpwm approximates a sinewave with large
carrier harmonics
Inductor reduces the effect of the carrier
harmonics
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PWM
Consider one leg only care must be taken not to switch Q1
and Q2 simultaneously a lockout delay is introduced between
the switching off of 1 device and the switching on of its partner
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Sa Sb Ia Vax Conducting Device
1 0 + Vdc/2 Q1
1 0 - Vdc/2 D1
0 1 + -Vdc/2 D2
0 1 - -Vdc/2 Q2
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PWM
Vax, Vbx and Vcx are switched between Vdc/2 and Vdc/2
and have pulse widths which vary sinusoidally at the desired
frequency pulsewidth modulation (PWM)
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PWM
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Modulation and
Carrierwaves for PWM
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0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-1
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-0.5
0
0.5
1
1.5
PWMOutput
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PWM Spectrum
A typical spectrum of VAX would look like:
0.2
0.25
0.3
0.35
0.4
0.45
onicamplitude
output voltage spectrum
fundamental
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0 10 20 30 40 50 60 70 80 90 1000
0.05
0.1
0.15
harmonic
h
arm carrier and sidebands
second carrier and sidebands
Would probably employ a passive shunt bandpass
filter tuned to the switching frequency
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ABB Statcom
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STATCOM connected to 32kV secondary bus
95MVA
Series connection of IGBTs
Diode Clamped Converters