Distributed hierarchical control structure for voltage harmonic compensation and harmonic current sharing in isolated MicroGrids

In this paper, a current sharing method based on the circular chain control (3C) method is proposed for controlling parallel inverters of unequal ratings in uninterruptible power supply (UPS) applications. Due to its circular structure, 3C is one of the most convenient methods which can be used in UPS as well as microgrid systems. However, the conventional 3C control strategy is only applicable to inverters of equal power ratings. The proposed method not only retains the circular structure of the 3C method, but also provides adaptability for the parallel operation of inverters with different power ratings. Moreover, this method adds hot-swap capability to the parallel inverter. A two-loop control structure is used to control the inverters. For proper current sharing, currents of inverters are conveyed in a circular structure with appropriate gains through control links. Simulation and experimental results for linear and nonlinear loads verify the effectiveness of the proposed strategy.

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A framework to model the STPA hierarchical control structure of an autonomous ship

Safety Science ◽

10.1016/j.ssci.2020.104939 ◽

2020 ◽

Vol 132 ◽

pp. 104939 ◽

Cited By ~ 1

Author(s):

Meriam Chaal ◽

Osiris A. Valdez Banda ◽

Jon Arne Glomsrud ◽

Sunil Basnet ◽

Spyros Hirdaris ◽

...

Keyword(s):

Control Structure ◽

Hierarchical Control ◽

Autonomous Ship

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Hierarchical Control Structure in Flexible Manufacturing Systems

Proceedings of the Twenty-Seventh International Matador Conference ◽

10.1007/978-1-349-09912-2_10 ◽

1988 ◽

pp. 61-66 ◽

Cited By ~ 1

Author(s):

C. C. Brown ◽

R. Leonard

Keyword(s):

Flexible Manufacturing ◽

Flexible Manufacturing Systems ◽

Manufacturing Systems ◽

Control Structure ◽

Hierarchical Control

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The Hierarchical Control Algorithm for DC Microgrid Based on the Improved Droop Control of Fuzzy Logic

Energies ◽

10.3390/en12152995 ◽

2019 ◽

Vol 12 (15) ◽

pp. 2995 ◽

Cited By ~ 4

Author(s):

Liang Zhang ◽

Kang Chen ◽

Shengbin Chi ◽

Ling Lyu ◽

Guowei Cai

Keyword(s):

Fuzzy Logic ◽

Control Algorithm ◽

Voltage Drop ◽

Hierarchical Control ◽

Voltage Regulation ◽

Droop Control ◽

Dc Microgrid ◽

Current Sharing ◽

The Difference ◽

Bus Voltage

In the direct current (DC) microgrid composed of multiple distributed generations, due to the different distances between various converters and the DC bus in the system, the difference of the line resistance will reduce the current sharing accuracy of the system. The droop control was widely used in the operation control of the DC microgrid. It was necessary to select a large droop coefficient to improve the current sharing accuracy, but a too large droop coefficient will lead to a serious bus voltage drop and affect the power quality. In view of the contradiction between the voltage regulation and load current sharing in the traditional droop control, a hierarchical control algorithm based on the improved droop control of the fuzzy logic was proposed in this paper. By improving the droop curve, the problems of voltage regulation and current sharing were solved simultaneously. The effectiveness of the algorithm was verified by simulation.

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Unbalanced Current Sharing Control in Islanded Low Voltage Microgrids

Energies ◽

10.3390/en11102776 ◽

2018 ◽

Vol 11 (10) ◽

pp. 2776 ◽

Cited By ~ 7

Author(s):

Foad Najafi ◽

Mohsen Hamzeh ◽

Matthias Fripp

Keyword(s):

Output Power ◽

Control Structure ◽

Nonlinear Loads ◽

Negative Sequence ◽

Current Sharing ◽

Current Controller ◽

Voltage Controller ◽

Zero Sequence ◽

Resonant Controller ◽

Virtual Impedance

This paper reports a new control strategy to improve sharing of unbalanced currents in islanded LV microgrids. This technique provides fast and effective sharing of positive-, negative- and zero-sequence currents, and is the first example of zero-sequence current sharing in the literature. The controllers are designed in the stationary frame. The control structure consists of four loops: (1) the current controller; (2) the voltage controller; (3) the droop controller and the (4) negative and zero sequence current controllers. The output current is considered unknown for the controller and is added to the control system as a disturbance. The proposed controller features a high gain in fundamental and harmonic frequencies, hence a good voltage quality is obtained in the presence of unbalanced and nonlinear loads. To this aim, a proportional-resonant (PR) controller is adopted as the current controller. By using a multi-resonant controller as current controller, a unified control structure is obtained which is suitable for both grid-connected and islanded modes. The voltage controller is designed using a resonant controller so that the voltage can have low VUF and THD in the presence of unbalanced and nonlinear loads. Furthermore, in this paper, the droop method is applied to the control structure to share real and reactive powers. Simulation studies show that the conventional droop method cannot share the oscillatory part of the output power that is due to the presence of unbalanced loads in the microgrid. This paper relies on using zero and negative sequence virtual impedance controller to share the oscillatory part of output power. By using zero-sequence virtual impedance controller (ZSVIC) and negative-sequence virtual impedance controller (NSVIC), the zero and negative sequence currents in the microgrid are controlled and shared effectively. By compensating zero- and negative-sequence currents locally, the flow of these currents in the microgrid is minimized, and the overall power quality of the islanded LV microgrid is improved.

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