Comparison of methods for implementing virtual synchronous machine on inverters

Abstract

Virtual Synchronous Machine also called VISMA [1] is a control algorithm   to   make   an   inverter   operated   as   a   conventional electromechanical   synchronous   machine.   It   is   a   promising solution  to  overcome  the  problems  of  the  grid  stability  and quality, which have been exacerbated by increasing integration of distributed   generation   units   into   the   grid.   Compared   to   the conventional  power  plants,  in  which  the  synchronous  machine dominate,    the    distributed    generation    units    have    either significantly  smaller  or  no  rotating  mass  and  damping  effect. These  weaknesses  can  be  compensated  by  using  the  VISMA concept  and  thus  the  power  system  quality  will  be  improved. Furthermore,  the  penetration  level  of  the  DG  sources  won’t  berestricted any more.  Up  to  now  the  VISMA  was  implemented  by  using  a  voltage-to-current  model  on  a  hysteresis  controlled  inverter  [1][2][3].  This method  will  be  called  VISMA-Method  1  here.    Since  the  most products  of  inverters  in  the  market  are  PWM  controlled,  the VISMA-Method  1  cannot  be  easily  applied  on  these  inverters. Therefore, a new method is developed to implement the VISMA by  using  a  current-to-voltage  model  on  the  currently  widely applied  PWM  controlled  inverter.  This  new  method  is  called VISMA-Method  2  in  this  paper  and  will  be  compared  with  the VISMA-Method 1 by simulation results.