Synchronization of single phase power converters to grid

1. SYNCHRONIZATION OF SINGLE-
PHASE POWER CONVERTERS TO
GRID
SYED LATEEF UDDIN B110877EE
K. PRUDHVI KUMAR B110921EE
S. RAVI PRAKASH REDDY B110494EE
Y. ROHITH B110901EE

2.  The world electrical energy consumption is
continuously rising.
 Large centrally controlled conventional power
sources connected to the transmission system are
complemented or replaced with greater number of
small renewable energy sources directly connected
to the local distribution grid.
 Power electronics converters serve as an efficient
interface between primary energy sources and the
utility grid.

3.  The power converters cannot be considered as simple grid-
connected equipment since they keep an interactive
relationship with the grid and can actively participate in
supporting the grid frequency and voltage, mainly when high
levels of power are considered for the power converters.
 Grid synchronization is a fundamental issue in the connection
of power converters to the grid.

4. There are two basic grid synchronization methods:
1. Frequency-domain detection methods:
Frequency-domain detection methods are based on some
discrete implementation.
2. Time-domain detection methods:
The time domain detection methods are based on some kind
of adaptive loop that enables an internal oscillator to track
the component of interest of the input signal.

5. •
•
•

6. •
•

7. BASIC STRUCTURE OF A PHASE-LOCKED LOOP
Three Basic blocks:
1.Phase Detector (PD)
2.Loop Filter (LF)
3.Voltage Controlled Oscillator (VCO)
Phase
Detector
Loop
Filter
Voltage
Controlled
Oscillator
fvv
vdv

8. PHASE LOCKED LOOP TUNING
cos( )x
p ik k 
 ok
dk

c
esdv sin in inA t  
PD LF
VCO


 sin ωin in inv A t 
 cos ωVCO c outv t 
Reference:
VCO output:
PD/Mixer output:          sin ω cos ω sin sin
2
d
d d in in c out in c in out in c in out
Ak
v Ak t t t t                    
VCO angle: c o e out o et k s dt k s dt       
if , then ,inωc      sin 2 sin
2
d
d in in out in out
Ak
v t          
in out       sin 2
2
d
d in in in out
Ak
v t        
The average value is  
2
d
d in out
Ak
v   
   sin in out in out    if , then ,

9. The hold range ΔwH
The pull-in range ΔwP
The lock range ΔwL
The pull-out range Δwpo

10. When the PLL is locked, the high frequency oscillations in the
phase error signal are only twice the input frequency. With
these very close frequencies, the assumption about a complete
cancellation of high-frequency term of phase-error signal by
the LF can no longer be acceptable.
Therefore, a new PD, different to the simple multiplier PD
should be used in order to cancel out oscillations at twice the
grid frequency in the phase-angle error signal.

11. What is the need of Orthogonal Component?
• To eliminate the 2° harmonic oscillation from
• And obtain .
Vd = Vsin(ωt+ φin) cos(ωt+ φout) - V cos(ωt+ φin) sin(ωt+ φout)
= Vsin(φin – φout)
   sin 2 sin
2
d
d in in out in out
Ak
v t        
 sin
2
d
in out
Ak
   
1
1p
i
K
sT
 
 
 
X
X
cos
sin
s
1
in
 Vsin -in out 
 Vsin in int  
 Vcos in int  
in outt  
+++
-
The phase-angle error signal
resulting from this ideal in-
quadrature PD is given by,
Quadrature
signal
generator -

12. Vd = Vsin(φin – φout)
• According to this equation, the in-quadrature PD does not generate
any steady-state oscillatory term, which allows PLL bandwidth to
increase and overcomes the problems regarding calculation of the
PLL key parameters.

13. Methods to create the orthogonal
component
Transport Delay T/4
 The transport delay block is easily implemented with size set to one fourth
the number of samples contained in one cycle of the fundamental
frequency.
 This method works fine for fixed grid frequency. If the grid frequency is
changing with for ex +/-1 Hz, then the PLL will produce an error
 If input voltage consists of several frequency components, orthogonal
signals generation will produce errors because each of the components
should be delayed one fourth of its fundamental period.
1
1p
i
k
T s
 
 
 
esdv
LF VCO
1
s
c
qv

dqDelay
T/4
v
v



PD
inv
inv

14. Hilbert Transform
 The Hilbert transform, also called a ‘quadrature filter’, is a fascinating
mathematical tool that presents two main features:
1. It shifts ±90° the phase-angle of spectral components of the input signal
depending on the sign of their frequency.
2. It only affects the phase of the signal and has no effect on its amplitude at
all.
 The time domain expression of the Hilbert transform of a given input signal
𝑣 is defined as
H(𝑣) =
1
𝜋 −∞
∞ 𝑣(𝜏)
𝑡−𝜏
𝑑𝜏 =
1
𝜋𝑡
* 𝑣
 Which describes the convolution product of the function h(t)=1/πt with the
signal 𝑣(𝑡).

15. Inverse Park Transformation
 A single phase voltage (vα) and an internally generated signal (vβ’) are
used as inputs to a Park transformation block (αβ-dq). The d axis output
of the Park transformation is used in a control loop to obtain phase and
frequency information of the input signal.
 vβ’ is obtained through the use of an inverse Park transformation,
where the inputs are the d and q-axis outputs of the Park
transformation (dq-αβ). fed through first-order low pass filters.
1
1p
i
k
T s
 
 
 
esdv
LF VCO
1
s
c
qv

dq
v
v



PD
inv
inv

dq
LPF
LPF
dv
qvv

v


16. A detailed study was made on synchronizing single phase
power converters to the power grid.
In particular, we studied various PLL based grid synchronizing
techniques including basic PLL and PLL based on In-quadrature
signals.

17. Further study has to be done for synchronizing single-phase
power converters to grid using PLLs based on adaptive filtering
from which quadrature signal can be successfully generated.
These adaptive filtering techniques include The Enhanced PLL,
Second Order Adaptive Filter, Second Order Generalized
Integrator and The SOGI PLL.

18. THANK YOU