Analysis and Design of Hybrid Harmonic Suppression Scheme for VSG Considering Nonlinear Loads and Distorted Grid BTech EEE Academic projects

ABSTRACT:

 The power quality of virtual synchronous generator (VSG) inevitably deteriorates in the presence of local nonlinear loads and distorted grid. In this paper, the conflict involved in the simultaneous elimination of distortion for both the inverter local load voltage and the grid exchanged current is first described. A unified control structure is presented that enables a tunable tradeoff between the two constrained harmonic sources. Then, a hybrid harmonic suppression scheme is proposed to enable the further improvement of the adaptability of VSG, which mainly consists of a local voltage harmonic control loop and an adaptive grid current-controlled loop. The local voltage harmonic control loop aims to scale down the inverter output impedance via a negative feedback loop, while the grid current-controlled compensator is intended to counteract the adverse effects from a weak grid via an additional voltage, which leads to substantially lower total harmonic distortion for both the local load voltage and the grid current at the same time. Small-signal modelling is performed to investigate the system stability and its robustness to parameter perturbations. The effectiveness of the proposed methodology is verified using hardware-in-the-loop simulations.

KEYWORDS:

  1. Distorted grid
  2. Harmonic suppression
  3. Harmonic observer
  4. Nonlinear load
  5. Virtual synchronous generator

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Structural diagram of grid-connected DG

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results of voltage and current harmonics suppression. (a) Results without harmonic suppression. (b) Results with proposed voltage control loop only. (c)Results with proposed hybrid harmonic suppression method.

Fig. 3 Simulation results of the robustness against Lg variation. (a) Results without harmonic suppression. (b) Results with proposed voltage control loop only. (c)Results with proposed hybrid harmonic suppression method.

Fig. 4 Simulation results of the robustness to load variation of the proposed method. (a) Before load increases. (b) With increased linear load. (c) With increased nonlinear load. (d) Linear load current.

Fig. 5 Simulation results of the robustness to load variation of the comparison method. (a) Before load increases. (b) With increased linear load. (c) With increased nonlinear load. (d) Linear load current.

CONCLUSION:

In view of the inherent contradiction involved in attenuating adverse effects in the presence of nonlinear loads and distorted grid, this paper presents tunable tradeoff between constrained harmonic sources. A hybrid harmonic suppression scheme is then proposed and consists of a local voltage harmonic control loop and an adaptive grid current-controlled loop, with a concurrent distortion inhibition capability. Compared with the existing approaches, the proposed methodology provides high-quality power supplies for both the grid and local loads.

REFERENCES:

[1] Q. Zhong, and G. Weiss, “Synchronverters: inverters that mimic synchronous generators,” IEEE Trans. Ind. Electron., vol. 58, no. 4, pp. 1259-1267, Apr. 2011.

[2] J. Ailpoor, Y. Miura, and T. Ise, “Power system stabilization using virtual synchronous generator with alternating moment of inertia,” IEEE Journal Emerg. Sel. Topics Power Electron., vol. 3, no. 2, pp. 451-458, June 2014.

[3] J. Liu, Y. Miura, and T. Ise, “Comparison of dynamic characteristics between virtual synchronous generator and droop control in inverter-based distributed generators,” IEEE Trans. Power Electron., vol. 31, no. 5, pp. 3600-3611, May 2016.

[4] D. Arricibita, P. Sanchis, and L. Marroyo, “Virtual synchronous generators classification and common trends”, in Proc. IECON, 2016, pp. 2433-2438.

[5] J. Fang, Y. Tang, H. Li, and X. Li, “A battery/ultra-capacitor hybrid energy storage system for implementing the power management of virtual synchronous generators,” IEEE Trans. Power Electron., vol. 33, no. 4, pp. 2820-2824, Apr. 2018.

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