Patent ID: 11967825
Assignee: HEFEI UNIVERSITY OF TECHNOLOGY
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H  G | IPC G  H

Claim 0:
1. A stability control method for a virtual synchronous generator (VSG) in a strong grid based on an inductance-current differential feedback, wherein
a topological structure of a VSG using the control method comprises a direct-current (DC)-side voltage source, a three-phase inverter, a three-phase grid impedance and a three-phase grid;
the DC-side voltage source is connected to the three-phase inverter, and the three-phase inverter is connected to the three-phase grid through the three-phase grid impedance;
the three-phase inverter is composed of a three-phase full-bridge inverter circuit, a three-phase inductance-capacitance (LC) filter, a three-phase voltage-current sensor, and a three-phase inverter controller;
the three-phase full-bridge inverter circuit is connected to the three-phase LC filter;
the three-phase voltage-current sensor samples three-phase voltages of a filter capacitance and three-phase currents of a filter inductance in the three-phase LC filter, and transmits a sampled signal to the three-phase inverter controller; and
the three-phase inverter controller performs control and computation, and outputs a pulse width modulation (PWM) signal to control the three-phase full-bridge inverter circuit;
the stability control method in the strong grid comprises a round of computation for controlling the VSG and a round of computation for controlling the inductance-current differential feedback in each computation cycle Tcompute of the three-phase inverter compute controller, wherein Tcompute=1/fcompute, and fcompute is a computed frequency of the three-phase inverter controller; and
the round of computation for controlling the VSG and the round of computation for controlling the inductance-current differential feedback comprise the following steps:
step 1: respectively labeling the filter capacitance and the filter inductance in the three-phase LC filter as an inverter-side filter capacitance and an inverter-side filter inductance, wherein the three-phase voltage-current sensor samples the three-phase voltages Ua, Ub, Uc of the inverter-side filter capacitance and the three-phase currents ILa, ILb, ILc of the inverter-side filter inductance, and transmits a sampled signal to the three-phase inverter controller;
step 2: obtaining, by the three-phase inverter controller, according to the three-phase voltages Ua, Ub, Uc of the inverter-side filter capacitance in step 1, two-phase voltages Uα, Uβ of the inverter-side filter capacitance in a static coordinate system through an equation for transforming voltages in a three-phase static coordinate system into voltages in a two-phase static coordinate system; and obtaining, by the three-phase inverter controller, according to the three-phase currents ILa, ILb, ILc of the inverter-side filter inductance in step 1, two-phase currents ILα, ILβ of the inverter-side filter inductance in the static coordinate system according to an equation for transforming currents in the three-phase static coordinate system into currents in the two-phase static coordinate system;
step 3: obtaining, by the three-phase inverter controller, according to the two-phase voltages Uα, Uβ of the inverter-side filter capacitance in the static coordinate system and the two-phase currents ILα, ILβ of the inverter-side filter inductance in the static coordinate system in step 2, an output active power P of the three-phase inverter and an output reactive power Q of the three-phase inverter through an equation for computing an instantaneous power,
the equation for computing the instantaneous power being:

P=UαILα+UβILβ

Q=UβILα−UαILβ

step 4: labeling a reactive power axis as a q-axis and an active power axis as a d-axis; and obtaining, by the three-phase inverter controller, according to the two-phase voltages Uα, Uβ of the inverter-side filter capacitance in the static coordinate system in step 2, a d-axis voltage Ud of the inverter-side filter capacitance and a q-axis voltage Uq of the inverter-side filter capacitance through an equation for transforming the voltages in the two-phase static coordinate system into voltages in a two-phase rotating coordinate system, and obtaining a phase angle θPLL of an A-phase voltage of the inverter-side filter capacitance through a phase-locked equation of a phase-locked loop (PLL) in a single synchronous coordinate system;
step 5: obtaining, by the three-phase inverter controller, according to the output active power P of the three-phase inverter in step 3, an angle θm of a modulated wave output from the VSG through an equation for computing an active power loop; and obtaining, by the three-phase inverter controller, according to the output reactive power Q of the three-phase inverter in step 3 and the d-axis voltage Ud of the inverter-side filter capacitance in step 4, an amplitude Um_VSG of the modulated wave output from the VSG through an equation for calculating a reactive power loop,
the equation for computing the active power loop being:, θ
   m
  
  =
  
   
    
     P
     set
    
    -
    P
    +
    
     
      ω
      n
      2
     
     ⁢
     
      D
      p
     
    
   
   
    
     J
     ⁢
     
      ω
      n
     
     ⁢
     
      s
      2
     
    
    +
    
     
      ω
      n
     
     ⁢
     
      D
      p
     
     ⁢
     s
    
   
  
 

the equation for computing the reactive power loop being:, U
   m_VSG
  
  =
  
   
    1
    
     
      K
      q
     
     ×
     s
    
   
   [
   
    
     
      D
      q
     
     ×
     
      (
      
       
        U
        nAmp
       
       -
       
        U
        d
       
      
      )
     
    
    +
    
     (
     
      
       Q
       set
      
      -
      Q
     
     )
    
   
   ]
  
 

wherein, Pset is a set value of the output active power of the three-phase inverter, ωn is a rated angular frequency of the three-phase grid, Dp is a frequency droop coefficient of the VSG, J is a virtual rotational inertia of the VSG, UnAmp is a rated phase voltage amplitude of the three-phase grid, Qset is a set value of the output reactive power of the three-phase inverter, Dq is a voltage droop coefficient of the VSG, Kq is an inertia coefficient for controlling the reactive power, and S is a Laplace operator;
step 6: obtaining, by the three-phase inverter controller, according to the amplitude Um_VSG of the modulated wave output from the VSG and the angle θm of the modulated wave output from the VSG in step 5, output three-phase modulation voltages UmA_VSG, UmB_VSG, UmC_VSG of the VSG through an equation for computing the modulated wave of the VSG,
the equation for computing the modulated wave of the VSG being:, U
    mA_VSG
   
   =
   
    
     U
     m_VSG
    
    ×
    
     cos
     ⁡
     (
     
      θ
      m
     
     )
    
   
  
  ⁢
  

  
   
    U
    mB_VSG
   
   =
   
    
     U
     m_VSG
    
    ×
    
     cos
     ⁡
     (
     
      
       θ
       m
      
      -
      
       
        2
        3
       
       ⁢
       π
      
     
     )
    
   
  
  ⁢
  

  
   
    U
    mC_VSG
   
   =
   
    
     U
     m_VSG
    
    ×
    
     cos
     ⁡
     (
     
      
       θ
       m
      
      +
      
       
        2
        3
       
       ⁢
       π
      
     
     )
    
   
  
 

step 7: obtaining, by the three-phase inverter controller, according to the three-phase currents ILa, ILb, ILc of the inverter-side filter inductance in step 1, increments ΔUmA, ΔUmB, ΔUmC of the output three-phase modulation voltages caused by a virtual series-connection inductance through an equation for computing the inductance-current differential feedback, the equation for computing the inductance-current differential feedback being:

ΔUmA=−sLvirILa 

ΔUmB=−sLvirILb 

ΔUmC=−sLvirILc 

wherein, Lvir is the virtual series-connection inductance;
step 8: computing, by the three-phase inverter controller, according to the output three-phase modulation voltages UmA_VSG, UmB_VSG, UmC_VSG of the VSG in step 6 and the increments ΔUmA, ΔUmB, ΔUmC of the output three-phase modulation voltages caused by the virtual series-connection inductance in step 7, output three-phase modulation voltages UmA, UmB, UmC of the three-phase inverter through a following computational equation:

UmA=UmA_VSG+ΔUmA 

UmB=UmB_VSG+ΔUmB 

UmC=UmC_VSG+ΔUmC, and

step 9: controlling, by the three-phase inverter controller, according to the output three-phase modulation voltages UmA, UmB, UmC of the three-phase inverter in step 8, transmission of a PWM modulated wave and outputting a PWM signal, and controlling the three-phase full-bridge inverter circuit through the PWM signal to transmit output electrical energy of the three-phase inverter to the three-phase grid.