IEEE 2011 Electrical Power and Energy Conference

Presenter:  Dr.  Francis  A.  Okou  

Royal  Military  College  of  Canada,  ECE  Department  

A  Mul@variable  Adap@ve  Nonlinear  Controller  for  a  Five-­‐Level  Diode  

Clamped  Statcom  

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IEEE 2011 Electrical Power and Energy Conference

Presenta@on  Outline  

1  –  Introduc@on    2  –  State  Space  Model  for  a  DCC  StatCom  

3  –  Controller  Design  

4  –  Simula@ons  &  Results  

5  -­‐  Conclusions  

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IEEE 2011 Electrical Power and Energy Conference

Objec@ves  •  To  propose  a  general  methodology  for  the  design  of  a  control  system  for  a  sta@c  compensator  that  uses  a  voltage  source  mul@level  diode  clamped  converter.  

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•  A  model  based  and  systema@c  design  approach  is  inves@gated.  

IEEE 2011 Electrical Power and Energy Conference

Transmission  line  compensa@on  •  Transmission  line  compensa@on  can  significantly  improve  the  efficiency  of  power  systems  

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•  U@lisa@on  of  mul@level  SVC  could  reduce  the  cost  and  the  complexity  of  the  compensator.  

•  Instability  associated  to  the  DC  bus  capacitor  voltages  is  an  significant  issue  for  this  MDCC.  

IEEE 2011 Electrical Power and Energy Conference

The  5-­‐level  DCC    5  

•  An  auxiliary  circuit  is  aXached  to  the  DC-­‐bus  .  

IEEE 2011 Electrical Power and Energy Conference

StatCom  Model  Capacitors  and  Auxiliary  Circuit  Models  

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The upper capacitor, lower capacitor and the auxiliary circuit inductor currents relationships must be considered.

The voltage relationship gives the following equation

IEEE 2011 Electrical Power and Energy Conference

StatCom  Model  Capacitors  and  Auxiliary  Circuit  Models  

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The upper capacitor and lower capacitor voltage-current relationships are

The current relationship between units (k) and (k+1) capacitors and inductors.

IEEE 2011 Electrical Power and Energy Conference

StatCom  Model  Capacitors  and  Auxiliary  Circuit  Models  

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The active power balance equation between the AC side and the DC side

IEEE 2011 Electrical Power and Energy Conference

Capacitors  and  Auxiliary  Circuit  Models  

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Capacitor voltage differences and inductance currents are used as state variables

IEEE 2011 Electrical Power and Energy Conference

StatCom  Model  AC/DC  Converter  Model  

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The converter AC-side is represented by the following equation

The previous equation can be expressed in the d-q reference frame as follows

IEEE 2011 Electrical Power and Energy Conference

StatCom  Model  

AC/DC  Converter  Model  

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the relationship between the grid voltage and the converter terminal voltage is:

A variable that represents the integral of the voltage deviation is introduced for the design.

IEEE 2011 Electrical Power and Energy Conference

StatCom  Control  Design  

The  proposed  Controller  has  two  components.  A  mul@variable  auxiliary  circuit  controller  and  a  mul@variable  terminal  voltage.  

The  auxiliary  circuit  controller  is  used  to  equalize  the  DC-­‐bus  capacitor  voltages.  

The  terminal  voltage  controller  maintains  the  StatCom  terminal  voltage  close  to  the  nominal  value.  

     

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IEEE 2011 Electrical Power and Energy Conference

StatCom  Control  Design  

A  model  based  design  approach  is  employed  to  obtain  the  control  laws.  

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Models  used  to  find  each  controller  structure  are:  

IEEE 2011 Electrical Power and Energy Conference

StatCom  Control  Design  

For  the  design  of  the  auxiliary  circuit  controller  

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IEEE 2011 Electrical Power and Energy Conference

StatCom  Control  Design  

For  the  design  of  the  terminal  voltage  controller  

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IEEE 2011 Electrical Power and Energy Conference

StatCom  Control  Design  The  input-­‐output  lineariza@on  design  scheme  is  employed  to  find  the  linearizing  control  laws  

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The  auxiliary  controls  are  selected  to  stabilise  the  system.  

IEEE 2011 Electrical Power and Energy Conference

StatCom  Control  Design  The  auxiliary  controls  include  a  linear  component  to  locally  stabilize  the  system  and  nonlinear  components  to  increase  the  stability  region.  

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Contrary  to  the  conven@onal  i/o  lineariza@on  method,  the  proposed  method  employs  all  the  state  variables.    

IEEE 2011 Electrical Power and Energy Conference

StatCom  Control  Design  Adapta@on  module  is  included  in  the  controller  to  guarantee  the  system  performance  when  the  opera@ng  condi@on  changes.  

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The  parameter  that  represents  power  losses  associated  to  the  converter  is  es@mated.  

IEEE 2011 Electrical Power and Energy Conference

Simula@ons  &  Results  The  StatCom    control  system  

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IEEE 2011 Electrical Power and Energy Conference

Simula@ons  &  Results  

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Two  tests  are  performed  -­‐  Auxiliary  circuits  are  disconnected  and  reconnected  

-­‐  The  grid  voltage  is  increased  in  one  area.  

IEEE 2011 Electrical Power and Energy Conference

Simula@ons  &  Results  

Valida@on  of  the  auxiliary  circuit  controller  

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Lea  picture  is  when  the  auxiliary  circuit  is  not  used  Right  picture  is  when  the  auxiliary  circuit  is  reconnected.  

IEEE 2011 Electrical Power and Energy Conference

Simula@ons  &  Results  

•  The  StatCom  performance  

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The  terminal  voltage  returns  to  its  nominal  value.  The  reac@ve  power  absorbed  by  the  StatCom  increases.  

IEEE 2011 Electrical Power and Energy Conference

Simula@ons  &  Results  •  The  StatCom  performance  

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Ac@ve  power  absorbed  by  the  StatCom    and  the  reac@ve  power  generated  by  the  source  remain  unchanged.  

IEEE 2011 Electrical Power and Energy Conference

Conclusions  

•  The  paper  has  proposed  a  general  and  systema@c  procedure  for  the  design  of  a  mul@level  StatCom  

•  A  general  state  space  model  is  proposed  for  a  diode  clamped  converter  that  has  an  auxiliary  circuit  connected  to  the  DC-­‐bus.  

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IEEE 2011 Electrical Power and Energy Conference

Conclusions  

•  A  control  system  that  has  2  components  is  proposed  for  the  mul@level  StatCom  – A  mul@variable  controller  for  the  auxiliary  circuit  to  balanced  the  capacitor  voltages.  

– A  mul@variable  controller  to  maintain  the  SatCom  terminal  voltage  close  to  the  nominal  value.  

• Simula@on  results  show  that  the  proposed  StatCom  performs  very  well.  

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