Abstract
This paper proposes an improved droop control strategy based on changeable reference in low-voltage microgrids. To restore running frequency of distributed generation to a rated value without affecting its reactive power output, changeable frequency reference, mainly compensating for frequency deviation, are proposed corresponding to various load demands. In terms of active power sharing inaccuracy associated with mismatched line impedance, changeable voltage amplitude reference is proposed to obtain a droop line suitable for the actual voltage of distributed generations. By further improvement of the active droop coefficient, power sharing is accurate with a difference in actual voltages of distributed generations. Virtual negative inductance is used to neutralize the redundant line inductance for strictly improving sharing accuracy. A robust control method based on Lyapunov function is used to handle the robustness problem in case of load variation. The control scheme is entirely decentralized, so communication links among distributed generations are redundant. Finally, simulation studies demonstrate the effectiveness of a control strategy.
Highlights
Distributed generation technology, as a research direction of new energies development, refers to distributed generation devices (DGs) resettled directly into distributed networks or near loads, including the micro-turbine, photo-voltaic cell, wind turbine and fuel cell, etc. [1,2]
An autonomous power system consisting of various DGs, energy storage units, loads and its control system is called a microgrid and can effectively integrate DGs to maintain a stable power supply for loads [4,5,6,7]
Two methods are verified: method 1 uses the constant frequency reference; Figure 9 shows the performance of reactive power and frequency in case of load variation
Summary
Distributed generation technology, as a research direction of new energies development, refers to distributed generation devices (DGs) resettled directly into distributed networks or near loads, including the micro-turbine, photo-voltaic cell, wind turbine and fuel cell, etc. [1,2]. Changeable reference, used in P/U droop control, is firstly proposed in this paper to realize frequency restoration and accurate active power sharing in low-voltage microgrids. For a DG in the microgrid, the equivalent circuit of its grid-connected state is shown, where UDG ∠δ is DG voltage; S is DG powers output; US ∠0◦ is bus voltage; X L , R L are line impedance; io is line current; X I , R I are inverter impedance whose values rely on the control demands when necessary (e.g., neutralize line inductance in this paper). A microgrid with mismatched line impedance, DG (e.g.,isDG1, poorly adjusted in the stabilization performance of running frequency, and frequency restoration is as DG2) voltages are unequal ( U1 U2 ) substituted into (8) and (10), and derive necessary.
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