Improved DC-Link Voltage Regulation Strategy for Grid-Connected Converters Academic Projects in Electrical

ABSTRACT:

In this paper, an improved dc-link voltage regulation strategy is proposed for grid-connected converters applied in dc microgrids. For the inner loop of the grid connected converter, a voltage modulated direct power control is employed to obtain two second-order linear time invariant systems, which guarantees that the closed-loop system is globally exponentially stable. For the outer loop, a sliding mode control strategy with a load current sensor is employed to maintain a constant dc-link voltage even in the presence of constant power loads at the dc-side, which adversely affect the system stability. Furthermore, an observer for the dc-link current is designed to remove the dc current sensor at the same time improving the reliability and decreasing the cost. From both simulation and experimental results obtained from a 15-kVA prototype setup, the proposed method is demonstrated to improve the transient performance of the system and has robustness properties to handle parameter mismatches compared with the inputoutput linearization method.

KEYWORDS:

  1. Dc microgrid
  2. Direct power control
  3. Grid connected converter
  4. Observer
  5. Sliding mode control

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Block diagram of the proposed control method (SMC with observer) for a rectifier system in the dc microgrid.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results when the dc load is changed from 460 W to 153 W. at 0.05 s and the reactive power is changed from 0 Var to 1 kVar at 0.75 s. (a) Real power; (b) reactive power; (c) is;c line current; (d) dc-link voltage.

Fig. 3. Simulation results when the dc load is changed from 460 W to 153 W at 0.05 s and vs;a has 10% sag. (a) Grid voltage; (b) is;c current; (c) dc-link voltage; (b) real and reactive power.

Fig. 4. Simulation results when the dc load is changed from 460 W to 153 W at 0.05 s and the THD of the grid voltage is 2.2%. (a) Grid voltage; (b) is;c current; (c) dc-link voltage; (b) real and reactive power.

CONCLUSION:

A three-phase PWM rectifier was controlled by the proposed control strategy, which has a dc-link current observer based SMC in the outer loop and a voltage modulated-DPC in the inner loop. The SMC was applied to generate the real power reference in the inner loop in order to make sure the dc link voltage to be within a certain level in the dc microgrids even there exist CPLs. Furthermore, an observer for the dc link current was designed in order to remove the need for a current sensor. Both simulation and experimental results show that the proposed method effectively reduces the overshoot of the dc-link voltage and is robust to parameter mismatch of the capacitance value in the dc-link.

REFERENCES:

[1] J. Liu, X. Lu, and J. Wang, “Resilience analysis of DC microgrids under denial of service threats,” IEEE Trans. Power Syst., vol. 34, no. 4, pp. 3199–3208, July 2019.

[2] F. Blaabjerg, M. Liserre, and K. Ma, “Power electronics converters for wind turbine systems,” IEEE Trans. Ind. Appl., vol. 48, no. 2, pp. 708– 719, 2012.

[3] B. Wei, Y. Gui, A. Marzabal, Trujillo, J. M. Guerrero, and J. C. Vasquez, “Distributed average secondary control for modular UPS systems based microgrids,” IEEE Trans. Power Electron., vol. 34, no. 7, pp. 6922–6936, July 2019.

[4] F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, “Overview of control and grid synchronization for distributed power generation systems,” IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1398–1409, 2006.

[5] M. Kazmierkowski and L. Malesani, “Current control techniques for three-phase voltage-source PWM converters: a survey,” IEEE Trans. Ind. Electron., vol. 45, no. 5, pp. 691–703, Oct 1998.

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