UDE-Based Current Control Strategy for LCCL-Type Grid-Tied Inverters

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)

SOFTWARE: MATLAB/SIMULINK

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.

Leave a Reply

Your email address will not be published.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