Comparison of Voltage Harmonic Identification Methods for Single-Phase and Three-Phase Systems

1. University of Alcalá Department of Electronics Comparison of Voltage Harmonic Identification Methods for Single-Phase and Three-Phase Systems R. Alcaraz, E.J. Bueno, S.Cóbreces, F.J. Rodríguez, C.Girón, F. Huerta Department of Electronics. University of Alcalá (Spain) raul.alcaraz@uclm.es emilio@depeca.uah.es M. Liserre Department of Electrical and Electronics Engineering Polytechnic of Bari (Italy) liserre@ieee.org Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

2. University of Alcalá Department of Electronics Contents • Introduction • Objectives • Single-Phase algorithms • Three-Phase algorithms • Experimental setup • Experimental results • Conclusions Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

3. University of Alcalá Department of Electronics Contents • Introduction • Objectives • Single-Phase algorithms • Three-Phase algorithms • Experimental setup • Experimental results • Conclusions Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

4. University of Alcalá Department of Electronics Introduction Voltage distorsion Increased losses and heating Missoperation of protective equipment Problem Nonlinear loads Harmonic Solutions Passive filters Active filters (AF) Isolated harmonic voltage Specific frequency Operation not limited to a certain load Resonances More difficult implementation More expensive Inject the undesired harmonic with 180º phase shift Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

5. University of Alcalá Department of Electronics Introduction • Harmonic identification (voltage or current) Active Filter • Synchronization Identification methods Voltage • Based on frequency-domain: • Discrete Fourier Transform (DFT) • Fast Fourier Transform (FFT) • Based on system model: • Kalman Filter • Based on transformations of frames Single-phase systems Current Three-phase systems Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

6. University of Alcalá Department of Electronics Contents • Introduction • Objectives • Single-Phase algorithms • Three-Phase algorithms • Experimental setup • Experimental results • Conclusions Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

7. uDC meas. L CDC PCC n uDC Grid voltage meas. ADC & SPLL pulses PWM generator Grid current meas. Harmonic identification Harmonic compensation uDC controller Current Controller University of Alcalá Department of Electronics Objectives • To obtain the exact information of the amplitude and phase of each harmonic. • To rebuilt exactly each harmonic. • Application: Active filters, feedforward of current controller for power converters. Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

8. University of Alcalá Department of Electronics Contents • Introduction • Objectives • Single-Phase algorithms • Detection based on DFT • Detection based on Wavelet • Detection based on Kalman Filter • Detection based on correlators in quadrature • Three-Phase algorithms • Experimental setup • Experimental results • Conclusions Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

9. c = 1 for positive seq. and -1 for negative seq. • θ(k) =ω1k-π/2 is the sPLLoutput. • γ is the sPLL delay University of Alcalá Department of Electronics Detection method based on DFT • The DFT of N1 points is carried out for each sample that arrives from the grid voltage signal. • The actual sample and N1 -1 previous samples are used, and for this reason the buffer N1 samples is necessary. • As the phase changes from one sample to the following sample, it is necessary the use of a Phase Loocked Loop (PLL), which recovers the instantaneous phase of the grid signal. Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

10. University of Alcalá Department of Electronics DFT: Experimental setup • Perfect identification. • In the worst cases, the response time is 2T1=40ms. • Correct operation under unbalanced grid voltages. • Run time depends on the identified harmonics, aprox. 120s. Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

11. University of Alcalá Department of Electronics Wavelet The Wavelet algorithm transforms the signal under investigation into another one that includes frequency and time domain informations. Multiresolution algorithms 5 levels Identification system (with family Daubechies40) Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

12. University of Alcalá Department of Electronics Wavelet: Simulation results Non-correct identification. Only it is possible to recover correctly the harmonics 1 and 5. Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

13. University of Alcalá Department of Electronics Kalman Filter • Characteristics • Optimal and robust estimation of magnitudes of sinusoids • Ability to track time-varying parameters • Synchronization of the two control blocks in the AF Covarianze for w(k) and v(k) State equation Measumerent equation 1st Kalman filter gain 4th Project ahead 2nd Update estimate with harmonic measumerent z(t) 3rd Compute error covariance Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

14. University of Alcalá Department of Electronics Kalman Filter: Continuous model State equation State equation Measumerent equation Constant A(k) Measumerent equation Constant B(k) x1(t) and x2(t) complementary x2(t) leads x1(t) 180º Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

15. University of Alcalá Department of Electronics Kalman Filter: Discrete model with variable reference s(k)= E(k)cos(ω1k+Φ(k)) = E(k)·cos(Φ(k))·cos(ω1k) - E(k)·sin(Φ(k))·sin(ω1k) x1(k)= E(k)·cos(Φ(k)) x2(k)= E(k)·sin(Φ(k)) In-phase component Quadrature-phase component State equation Noise-free voltage signal s(k) (n harmonics) • Ei(k) and Φi(k) amplitude of the phasor and phase of the ith harmonic • n harmonic order ω(k) time variation Measumerent equation State equation Measumerent equation v(k) high frequency noise B(k) time-varying vector Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

16. University of Alcalá Department of Electronics Kalman Filter: Discrete model with stationary reference s(k)= E(k)cos(ω1k+Φ(k)) x1(k)= E(k)·cos(ω1k + Φ(k)) x2(k)= E(k)·sin(ω1k + Φ(k)) At k+1 s(k+1)=E(k+1)·cos(ω1k+ ω1+Φ(k+1))= x1(k+1)= x1(k)cos(ω1) – x2(k)sin(ω1) x2(k+1)= E(k+1)·sin(ω1k+ ω1+Φ(k+1))= x2(k+1)= x1(k)sin(ω1) + x1(k)cos(ω1) State equation State equation Measumerent equation ω(k) time variation Constant B(k) Constant A(k) Measumerent equation v(k) high frequency noise Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

17. University of Alcalá Department of Electronics Kalman Filter: Identification Systems • Stationary reference • Variable reference and SPLL Identification block Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

18. University of Alcalá Department of Electronics Kalman Filter: Identification Systems • Variable reference and Time shift • Variable reference and SPLL B(k) depends on w1k! Solution: SPLL High peak voltages during transitory by the grid disturbances! Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

19. University of Alcalá Department of Electronics Kalman Filter: Identification Systems • Variable reference and Time shift k = k1 + k2 k2 delay between grid starts up and identification system is connected to the grid s(k)= E(k)cos(ω1k+ω1k2+Φ(k)) x1(k)= E(k)·cos(ΦM(k)) x2(k)= E(k)·sin(ΦM(k)) Φ1(k)=ΦM(k) Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

20. University of Alcalá Department of Electronics Kalman Filter: Experimental Results Selection of Kalman filter parameters CONTINUOUS DISCRETE MODEL STATIONARY REFERENCE DISCRETE MODEL VARIABLE REFERENCE Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

21. To make the system faster and simpler, the correlators in quadrature will be implemented by means of adapted filters,which are characterized to have an impulsive response h(k) =s(N1-k), being s(k) the signal that the corresponding correlator uses in the detection. Therefore, the impulsive responses of the used filters to identify the harmonic n are: University of Alcalá Department of Electronics Correlators in quadrature Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

22. University of Alcalá Department of Electronics Contents • Introduction • Objectives • Single-Phase algorithms • Three-Phase algorithms • Synchronous Reference Methods (SRF) • Instantaneous Reactive Power Theory (IRPT) • Experimental setup • Experimental results • Conclusions Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

23. HPF University of Alcalá Department of Electronics Synchronous Reference Method (SRF) Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

24. University of Alcalá Department of Electronics Instantaneous Reactive Power Theory (IRPT) • When the grid voltage signal is unbalanced, a non-correct harmonic identification is produced. • Due to the dq-components rotating in opposite directions, the voltage and current fundamental harmonic produce a dc-component plus ac-component in the instantaneous power therefore, harmonic distortion can not be recovered with a HPFand the inverse Park Transform Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

25. University of Alcalá Department of Electronics Contents • Introduction • Objectives • Single-Phase algorithms • Three-Phase algorithms • Experimental setup • Experimental results • Conclusions Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

26. Optical transmitters ADCs Interface Board Relays Optical receivers Link Board DIGILAB 2E TMS320C6713 DSK University of Alcalá Department of Electronics Experimental Setup Acquisition card Digital Signal Processing Glue logic DSP  TMS320C6713 with ADCs MAX1309 of 12 bits Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

27. University of Alcalá Department of Electronics Contents • Introduction • Objectives • Single-Phase algorithms • Three-Phase algorithms • Experimental setup • Experimental results • Conclusions Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

28. Improvement Factor (IF) • balanced grid • unbalanced grid • frequency deviations < 0.1% University of Alcalá Department of Electronics Experimental results: Comparison Criterions Transient Response Quality Related with the maximum peak level identified during a transitory due to disturbance in the grid PF=Vpident/Vpgrid  <15 Transient Response Time TRT Delay between a disturbance in the grid voltage and the system harmonic identification<100 ms Run Time Time that algorithms takes in its execution Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

29. University of Alcalá Department of Electronics Experimental results: Kalman Filter Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

30. University of Alcalá Department of Electronics Experimental results: Single-Phase Systems Drift frequency 0.1Hz Balanced grid voltages Unbalanced grid voltages Transient Response Quality Transient Response Time Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

31. Unbalanced grid voltages Balanced grid voltages Drift frequency 0.1Hz Transient Response Quality Transient Response Time Run Time University of Alcalá Department of Electronics Experimental results: Three-Phase Systems Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

32. University of Alcalá Department of Electronics Contents • Introduction • Objectives • Single-Phase algorithms • Three-Phase algorithms • Experimental setup • Experimental results • Conclusions Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

33. University of Alcalá Department of Electronics Conclusions • In the present work, an overview and comparison of different techniques for harmonics identification in single-phase and three-phase systems has been achieved. • As contribution, some modifications have been made on existing methods. Also, for the case of single-phase, the method based on correlators in quadrature have been proposed for the first time. • The identification technique more suitable for each situation depends the characteristics of the environment where this is used. • For single-phase the identification technique, that better results obtains, is the based on FFT and sPLL, since it obtains the best factors IF, TRT and PF. • On the other hand, for the three-phase systems, experimental results and simulation show that the synchronous harmonic dq-frame method (with the utilization of transformations realized in sPLL) is the best solution. This technique permits a selective filtering, obtains a correct operation with balanced, unbalanced grid signals, has an excellent dynamic response (as transient time and transient quality) and very reduced algorithm execution time. • The analysis have been validated by simulations and experimental results carried out with the digital signal processor TMS320C6713. Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006

34. University of Alcalá Department of Electronics Comparison of Voltage Harmonic Identification Methods for Single-Phase and Three-Phase Systems ACKNOWLEDGMENTS This work has been financied by the Spanish administration (ENE2005-08721-C04-01) R. Alcaraz, E.J. Bueno, S.Cóbreces, F.J. Rodríguez, C.Girón, F. Huerta Department of Electronics. University of Alcalá (Spain) raul.alcaraz@uclm.es emilio@depeca.uah.es M. Liserre Department of Electrical and Electronics Engineering Polytechnic of Bari (Italy) liserre@ieee.org Researching group in Electronic Engineering applied to the Renewable Energies IECON 2006