A NOVEL CONTROL STRATEGY FOR PARALLEL CONNECTED INVERTERS IN AUTONOMOUS AC MICROGRID
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Date
2022-09
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G. B. Pant University of Agriculture & Technology, Pantnagar-263145
Abstract
In the past few years, a conventional centralized grid structure has been shifting
towards a decentralized structure due to the availability of renewable energy-based
Distributed Generation (DG) units. But the management of these DG sources in the
distribution network is not an easy task due to the problems associated with the operation
and control. The control structure should be able to provide coordinated control with all
parallel connected DG units and achieve stable operation of the whole network. Especially
during autonomous mode, the control structure has to maintain and regulate the voltage and
frequency of the whole network and has to decide power sharing between parallel connected
DG units.
The droop-based control schemes measure locally available parameters and process
them to generate control signals. Based on load demand, droops are introduced in operating
voltage and frequency and operating set points are decided. Each DG unit regulates its
control parameter at local level. The advantage of this control is that by establishing stability
of a single unit at local level we can expect stability of the whole system at global level.
The concept of droop control for converter-based DG sources was derived from the
inherent property of the governor of synchronous generators. These synchronous generators
supply power to the load through transmission lines and the whole network is highly
inductive in nature. But DG based network is resistive in nature and due to the presence of
power electronic interface (e.g. converters etc.), these have low or no inertia. The
implementation of conventional droop controller in such a network leads to poor network
performance and slow response. High transients may occur in the system during disturbances
which might be high enough to damage or may cause mal-operation of equipments and
might make whole network unstable. To address drawbacks associated with conventional
droop control technique, this thesis presents a modified control scheme. The drawback
associated with conventional droop control strategy are identified through intensive analysis
in MATLAB/Simulink environment and an improved control strategy is proposed.
Performance is analyzed under varying loading conditions and integrating DG sources at
different time instants. Simulation results show that proposed control strategy is capable of
regulating voltage and frequency of the network according to the load demand. It improves
transient response of the system and provides a faster and more damped response to maintain
stable operation of the network.
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Theses of Ph.D