Grid Voltages Estimation for Three-Phase PWM Rectifiers Control Without AC Voltage Sensors

ABSTRACT

This paper proposes a new AC voltage sensor less control scheme for three-phase pulse width modulation rectifier. A new startup process to ensure a smooth starting of the system is also proposed. The sensor less control scheme uses an adaptive neural (AN) estimator inserted in voltage oriented control to eliminate the grid voltage sensors. The developed AN estimator combines an adaptive neural network in series with an adaptive neural filter. The AN estimator structure leads to simple, accurate and fast grid voltages estimation. And makes it ideal for low cost digital signal processor implementation. L y a p u n o v based stability and parameters tuning of the AN estimator are performed.

Simulation

Simulation and experimental tests are carried out to verify the feasibility and effectiveness of the AN estimator. Obtained results show that, the proposed AN estimator presented faster convergence and better accuracy than the second order generalized integrator based estimator. The new startup procedure avoided the over current and reduced the settling time. The AN estimator presented high performances even under distorted and unbalanced grid voltages.

BLOCK DIAGRAM:

Fig. 1. Overall structure of the developed AC voltage sensor less control.

EXPECTED SIMULATION RESULTS

Fig. 2. Steady state performances of the AN estimator in diode rectifier operation mode (experiment): (a) computed input voltages vαn and vβn, (b) actual AC line currents iα and iβ, (c) actual grid voltage eα, estimated grid voltage eα,est and estimation error and (d) actual grid voltage eβ, estimated grid voltage eβ,est and estimation error.

Fig. 3. Steady-state performances of the P LL in diode rectifier operation mode (experiment): (a) computed d q components (ed, e q) with actual grid  voltages and computed d q components (ed,est, e q,est) with estimated grid  voltages and (b) computed angles θ and θest with actual and estimated grid voltages, respectively.

Fig. 4. Performances of the AN estimator at startup (experiment): (a) input voltages vαn and vβn, (b) actual AC line currents iα and iβ, (c) reference and  measured DC link voltages (V dc ref, V dc), (d) actual grid voltage eα, estimated  grid voltage eα,est and estimation error and (d) actual grid voltage eβ, estimated grid voltage eβ,est and estimation error.

Fig. 5. Performances of the P LL at startup (experiment): (a) computed d q components (ed, e q) with actual grid voltages and computed d q components (ed,est, e q,est) with estimated grid voltages and (b) computed angles θ and θest with actual and estimated grid voltages, respectively.

Steady-state performances

Fig. 6. Transient performances of the AN estimator under dc ref step change (experiment): (a) actual grid voltage eα, estimated grid voltage eα,est and estimation error, (b) actual grid voltage eβ, estimated grid voltage eβ,est and estimation error, (c) actual AC line currents iα and iβ and (d) reference and measured DC link voltages.

Fig. 7. Transient performances of the P LL under V dc ref step change (experiment): (a) computed d q components (ed, e q) with actual grid voltages and computed d q components (ed,est, e q,est) with estimated grid voltages and (b) computed angles θ and θest with actual and estimated grid voltages, respectively.

Fig. 8. Transient performances of the AN estimator under load resistance variation (experiment): (a) actual grid voltage eα, estimated grid voltage eα,est and estimation error, (b) actual grid voltage eβ, estimated grid voltage eβ,est and estimation error and (c) actual AC line currents.

Fig. 9. Transient performances of the P LL under load resistance variation (experiment): (a) computed d q components (ed, e q) with actual grid voltages and computed d q components (ed,est, e q,est) with estimated grid voltages and (b) computed angles θ and θest with actual and estimated grid voltages, respectively.

Transient performances

Fig. 10. Transient performances of the AN estimator under symmetric grid voltages sag (experiment): (a) actual grid voltage eα, estimated grid voltage eα,est and estimation error and (b) actual grid voltage eβ, estimated grid voltage eβ,est and estimation error and (c) actual AC line currents.

Fig. 11. Transient performances of the P LL under symmetric grid voltages sag (experiment): (a) computed d q components (ed, e q) with actual grid voltages and computed d q components (ed,est, e  q,est) with estimated grid voltages and (b) computed angles θ and θest with actual and estimated grid voltages, respectively.

Transient performances

Fig. 12. Transient performances of the AN estimator under grid voltages unbalance (experiment): (a) actual grid voltage eα, estimated grid voltage eα,est and estimation error and (b) actual grid voltage eβ, estimated grid voltage eβ , est and estimation error and (c) actual AC line currents.

Fig. 13. Transient performances of the P LL under grid voltages unbalance (experiment): computed d q components (ed, e q) with actual grid voltages and computed d q components (ed,est, e q,est) with estimated grid voltages and (b) computed angles θ and θest with actual and estimated grid voltages, respectively.

Fig. 14. Transient performances of the AN estimator under distorted grid voltages (simulation): (a) actual grid voltage eα and estimated grid voltage eα,est, (b) actual grid voltage eβ and estimated grid voltage eβ,est and (c) actual AC line currents.

Fig. 15. Transient performances of the P LL under distorted grid voltages (simulation): computed d q components (ed, e q) with actual grid voltages and computed d q components (ed,est, e q,est) with estimated grid voltages and (b) computed angles θ and θest with actual and estimated grid voltages respectively.

CONCLUSION

In this work, a new AN estimator for eliminating the grid voltage sensors in V O C of three phase P WM rectifier has been proposed. The developed AN estimator combines estimation capability of the ANN and filtering property of the A NF. L y a p u no v’s theory based stability analysis has been exploited for optimal tuning of the AN estimator. Hence, simple, accurate and fast grid voltages estimation has been obtained. To avoid current overshoot and to reduce the settling time at the startup, a new startup process has been proposed to initialize the V O C. The effectiveness of the proposed procedure has been experimentally demonstrated.

comparison

A comparison between the proposed AN estimator and the recently developed SO GI based estimator has been conducted. This comparison has clearly indicated faster convergence and better accuracy of the proposed estimator. Finally, robustness of the AN estimator regarding to step change in DC link voltage reference, load resistance variation and non ideal grid voltages conditions (symmetrical sag, unbalance, distortion) has been investigated through simulation and experimental tests. The obtained results have demonstrated high performances of the proposed AN estimator within the analyzed working conditions.

REFERENCES

[1] R. Te o d o re s c u, M. L is er re, and P. Rodriguez, Grid converters for photo voltaic and wind power systems, John Wiley & Sons, 2011.

[2] A.-R. Ha it ham, M. Malinowski, and K. Al Had dad, Power electronics for renewable energy systems, transportation and industrial applications, John Wiley & Sons, 2014.

[3] T. Fried l i, M. Hart man n, and J. W. K o l a r, “The essence of three-phase PFC rectifier systems–Part e II,” IEEE Trans. Power Electron., vol. 29, no. 2, pp. 543–560, Feb. 2014.

[4] M. B. K e t z er and C. B. Jacob in a, “Sensor less control technique for P WM rectifiers with voltage disturbance rejection and adaptive power factor,” IEEE Trans. Ind. Electron., vol. 62, no. 2, pp. 1140–1151, Feb. 2015.

[5] A. Be ch o u c he, H. Se d d i k i, D. O u l d Ab d e s lam, and K. Mes bah, “Adaptive AC filter parameters identification for voltage oriented control of three phase voltage source rectifiers”, Int. J. Mod ell. Identification Control, vol. 24, no. 4, pp. 319–331, 2015.

[6] H. G h o l a mi-K he sh t and M. Mon fared, “Novel grid voltage estimation by means of the Newton–Rap h son optimization for three-phase grid
connected voltage source converters,” I ET Power Electron., vol. 7, no.
12, pp. 2945–2953, Dec. 2014.
[7] A. A. G hod k e and K. Chat t e r j e e, “One-cycle-controlled bidirectional
three-phase unity power factor ac–dc converter without having voltage
sensors,” I ET Power Electron., vol. 5, no. 9, pp. 1944–1955, Nov. 2012.

Leave a Reply

Your email address will not be published. Required fields are marked *