This paper proposes a new AC voltage sensorless 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 sensorless
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. Lyapunov based stability and parameters tuning of the AN
estimator are performed. 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.
KEYWORDS
1.
AC voltage
sensorless control
2.
Adaptive
neural (AN) estimator
3.
Grid voltages
estimation
4.
Neural
networks (NNs)
5.
Pulse-width
modulation (PWM) rectifier
6.
Startup process
7.
Voltage-oriented
control (VOC)
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Overall structure of the developed AC voltage sensorless 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 PLL in diode rectifier operation mode
(experiment): (a) computed dq components (ed, eq) with
actual grid voltages and computed dq components
(ed,est, eq,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 (Vdc
ref, Vdc), (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 PLL at startup (experiment): (a) computed dq components
(ed, eq) with actual grid voltages and computed dq components
(ed,est, eq,est) with estimated grid voltages and (b) computed
angles θ and θest with actual and estimated grid
voltages, respectively.
Fig.
6. Transient performances of the AN estimator under Vdc 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 PLL under Vdc ref step change (experiment):
(a) computed dq components (ed, eq) with actual grid
voltages and computed dq components (ed,est, eq,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 PLL under load resistance variation (experiment):
(a) computed dq components (ed, eq) with actual grid
voltages and computed dq components (ed,est, eq,est) with
estimated grid voltages and (b) computed angles θ and θest with actual and
estimated grid voltages, respectively.
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 PLL under symmetric grid voltages sag
(experiment): (a) computed dq components (ed, eq) with
actual grid voltages and computed dq components (ed,est, eq,est)
with estimated grid voltages and (b) computed angles θ and θest with actual and
estimated grid voltages, respectively.
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 PLL under grid voltages unbalance (experiment):
computed dq components (ed, eq) with actual grid voltages
and computed dq components (ed,est, eq,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 PLL under distorted grid voltages (simulation):
computed dq components (ed, eq) with actual grid voltages
and computed dq components (ed,est, eq,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 VOC
of three-phase PWM rectifier has been proposed. The developed AN estimator
combines estimation capability of the ANN and filtering property of the ANF.
Lyapunov’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 VOC. The effectiveness of the proposed procedure has been experimentally
demonstrated. A comparison between the proposed AN estimator and the recently
developed SOGI 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. Teodorescu, M. Liserre, and P. Rodriguez, Grid converters for photovoltaic
and wind power systems, John Wiley & Sons, 2011.
[2]
A.-R. Haitham, M. Malinowski, and K. Al-Haddad, Power electronics for
renewable energy systems, transportation and industrial applications, John
Wiley & Sons, 2014.
[3]
T. Friedli, M. Hartmann, and J. W. Kolar, “The essence of three-phase PFC
rectifier systems–Parte II,” IEEE Trans. Power Electron., vol. 29, no.
2, pp. 543–560, Feb. 2014.
[4]
M. B. Ketzer and C. B. Jacobina, “Sensorless control technique for PWM
rectifiers with voltage disturbance rejection and adaptive power factor,” IEEE
Trans. Ind. Electron., vol. 62, no. 2, pp. 1140–1151, Feb. 2015.
[5]
A. Bechouche, H. Seddiki, D. Ould Abdeslam, and K. Mesbah, “Adaptive AC filter
parameters identification for voltage-oriented control of three-phase
voltage-source rectifiers”, Int. J. Modell. Identification Control, vol.
24, no. 4, pp. 319–331, 2015.
