ABSTRACT:
LCL filter is usually used as an interface between inverters
and the grid. However, due to the characteristics of LCL filter and
system uncertainties, it is complex to design a controller with proper
parameters. In this paper, with LCCL filter, the order of the inverter
control system can be reduced from third order to first order, and an
uncertainty and disturbance estimator based control strategy for grid-tied
inverters with LCCL filter is proposed. Specifically, the proposed
control strategy consists of differential feed forward, proportional–integral
controller, and grid voltage feed forward. Moreover, with one-sampling
computation plus half-sampling pulse width modulation delays considered, a
simple and clear tuning algorithm for the proposed control strategy is
presented. Finally, the inverter system with the proposed control strategy is
investigated, and the effectiveness is supported by the tuning and comparative experiments
with a 2-kW inverter.
KEYWORDS:
1.
Current
control
2.
Inverter
3.
LCCL filter
4.
Tuning algorithm
5.
Uncertainty
and disturbance estimator (UDE)
CIRCUIT DIAGRAM:
Fig. 1. System topology of the grid-tied
inverter with LCCL filter.
.
EXPECTED SIMULATION RESULTS
Fig. 2. Result of UDE-based
control without grid voltage feed forward. (a) Injected grid current i2
. (b) Spectrum of the injected grid current.
Fig. 3. Tuning results of
UDE-based control with the same α = 10 000 rad/s, β = 5000
rad/s, and different k.
(a) k = 10 000 rad/s. (b) k = 9000 rad/s. (c) k = 7000
rad/s.
Fig. 4. Result
of UDE-based control under i*12 (s) = 10 A with α = 10
000 rad/s, β = 5000 rad/s, and k = 8000 rad/s. (a)
Injected grid current i2 .
(b) Spectrum of the injected grid current.
Fig. 5. Result
of PI control under i*12 (s) = 10 A with kp
= 17 and ki = 14400. (a) Injected grid current i2 . (b) Spectrum of the injected grid current.
CONCLUSION:
For grid-tied inverter, LCL filter is widely used
to attenuate the high switching frequency harmonics caused by PWM. However, due
to the characteristic of LCL filter and uncertainty, it
is complex to design a controller with proper parameters. In this paper, with LCCL filter, the inverter control system can be degraded from third
order to first order. And a UDE-based injected grid current control strategy
was built. The proposed strategy unified the system uncertainty and disturbance
into the lumped disturbances, and the closed-loop system adjusted by PI
regulator approached to the reference model. Meanwhile, the PI controller can
be expressed in the error feedback gain, the desired closed-loop bandwidth, and
the approximate lumped disturbance bandwidth. Moreover, with one-sampling
computation plus half-sampling PWM delays considered, a simple and clear tuning
algorithm for the proposed control strategy was provided. Finally, the proposed
strategy was verified by the tuning and comparative experiments on a 2-kW
inverter.
REFERENCES:
[1] M. Lindgren and J.
Svensson, “Control of a voltage-source converter connected to the grid through
an LCL-filter-application to active filtering,” in Proc. IEEE Power
Electron. Spec. Conf., May 1998, pp. 229–235.
[2] E. Twining and D. G. Holmes, “Grid current regulation of a
three-phase voltage source inverter with an LCL input filter,” IEEE
Trans. Power Electron., vol. 18, no. 3, pp. 888–895, May 2003.
[3] G. Shen, D. Xu, L. Cao, and X. Zhu, “An improved control
strategy for grid-connected voltage source inverters with an LCL filter,” IEEE Trans. Power Electron., vol. 23, no. 4, pp.
1899–1906, Jul. 2008.
[4] G. Shen, X. Zhu, J. Zhang, and D. Xu, “A new feedback method
for PR current control ofLCL-filter-based
grid-connected inverter,” IEEE Trans. Ind. Electron., vol. 57, no. 6,
pp. 2033–2041, Jun. 2010.
[5] R. P. Alzola, M. Liserre, F. Blaabjerg, R. Sebasti´an, J.
Dannehl, and F. W. Fuchs, “Analysis of the passive damping losses in LCL-filter-based grid converters,” IEEE Trans. Power Electron.,
vol. 28, no. 6, pp. 2642–2646, Jun. 2013.
