facts - statcom 2009

7/29/2019 Facts - Statcom 2009

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H64APCH64APC

FACTsFACTs and Distributedand Distributed

Power SystemsPower Systems

1

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,

2

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

3

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

4

to control Vpcc

Consider behaviour of a simple system in the

presence of a load change


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Phasor Diagrams

5


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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.

6


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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

9

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

13

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

14

STATCOM connected to 32kV secondary bus

95MVA

Series connection of IGBTs

Diode Clamped Converters

facts - statcom 2009

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