Abstract
The Grid-Connected Droop-Controlled Distributed Generations (GCDCDGs) are widely used in power systems. However, their power flow is very sensitive to the Upstream Grid (UG) frequency and voltage magnitude fluctuations. This paper focuses on the power and current limiting of inverter-interfaced GCDCDGs under UG frequency and/or voltage magnitude drops. GCDCDG output power and current increase under the UG frequency drop, and if this increase exceeds the maximum of them, current limiters are saturated and according to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P\sim \omega $ </tex-math></inline-formula> droop characteristic the GCDCDG frequency does not track the UG frequency, and this frequency difference leads to power oscillation between DG and UG and the system becomes unstable. In this paper, a new strategy based on the droop-control method is proposed to limit the output power and current of GCDCDGs without using a current limiter that realizes a stable operation under the mentioned conditions. In the proposed method instead of increasing the droop coefficients to limit <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> at their constraints, the droop curves move down after powers and currents exceed maximum values, using two supplementary control signals. The performance of the proposed method is demonstrated with simulation results using MATLAB/Simulink environment under several case studies.
Highlights
G RID-CONNECTED Distributed Generation (DGs) are extensively used to provide the demand of the consumers
This paper focuses on the current limiting of Grid-Connected Droop-Controlled Distributed Generations (GCDCDGs) in GCMGs while Upstream Grid (UG) frequency and/or voltage magnitude drop
A new strategy based on the droop-control method is proposed to limit the output currents of GCDCDGs without using current limiters which realizes a stable operation under the above-mentioned conditions
Summary
G RID-CONNECTED Distributed Generation (DGs) are extensively used to provide the demand of the consumers. A current-limiting droop controller has been proposed in [5] for single-phase grid-connected inverters that can operate under either normal or faulty grid conditions. A new strategy based on the droop-control method is proposed to limit the output currents of GCDCDGs without using current limiters which realizes a stable operation under the above-mentioned conditions. The proposed droop-control based power and current limiting strategy are discussed in detail. Block diagrams of proposed droop-control based power and current limiting strategy: (top) P and Iod limiter and (bottom) Q and Ioq limiter. To overcome the above-mentioned problems the proposed unified droop-control based current limiting strategy will be described as follows
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