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:
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[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.
