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Synchronization of single phase power converters to grid

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Synchronization of single phase power converters to grid

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Synchronization of single phase power converters to grid

  1. 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. 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. 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. 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. 5. • • •
  6. 6. • •
  7. 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. 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. 9. The hold range ΔwH The pull-in range ΔwP The lock range ΔwL The pull-out range Δwpo
  10. 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. 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. 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. 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. 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. 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. 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. 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. 18. THANK YOU

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