Dynamic Modeling of Microgrid for Grid Connected and Intentional Islanding Operation



 Microgrid is defined as the cluster of multiple distributed generators (DGs) such as renewable energy sources that supply electrical energy. The connection of microgrid is in parallel with the main grid. When microgrid is isolated from remainder of the utility system, it is said to be in intentional islanding mode. In this mode, DG inverter system operates in voltage control mode to provide constant voltage to the local load. During grid connected mode, the Microgrid operates  in constant current control mode to supply preset power to the main grid. The main contribution of this paper is summarized as

  • Design of a network based control scheme for inverter based sources, which provides proper current control during grid connected mode and voltage control during islanding
  • Development of an algorithm for intentional islanding detection and synchronization controller required during grid
  • Dynamic modeling and simulation are conducted to show system behavior under proposed method using

From the simulation results using Simulink dynamic models, it can be shown that these controllers provide the microgrid with a deterministic and reliable connection to the grid.


  1. Distributed generation (DG)
  2. grid connected operation
  3. intentional islanding operation and islanding detection
  4. Microgrid



Fig.1. Dynamic model of microgrid with controller.


Fig. 2. Line Current without current controller

Fig.3. Line Voltage without Voltage controller

Fig. 4. Line Voltage with voltage controller

Fig. 5. Phase voltage waveform (a) without re-closure controller (b) with re-closure controller

Fig. 6. Synchronization for grid reconnection (a) without re-closure algorithm (b) with re-closure algorithm


Current and voltage Control techniques have been developed for grid connected and intentional islanding modes of operation using PI controllers. An intentional islanding detection algorithm responsible for switching between current control and voltage control is developed using logical operations and proved to be effective. The reconnection algorithm coupled with the synchronization controller enabled the DG to synchronize itself with the grid during grid reconnection. The performance of the microgrid with the proposed controllers and algorithms  has been analyzed by conducting simulation on dynamic model using SIMULINK. The simulation results presented here confirms the effectiveness of the control scheme.


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A PLL Based Controller for Three Phase Grid Connected Power Converters

A PLL Based Controller for Three Phase Grid Connected Power Converters


The current control of three-phase grid-connected converters is typically carried out by using a proportional resonant controller or synchronous reference frame proportional integral regulator. The implementation of these controllers often requires knowledge of the grid voltage frequency/phase angle, which is typically provided by a synchronization unit. It implies that dynamics and possible inaccuracies of the synchronization unit have a considerable impact on the current controller performance. The aim of this letter is to design an adaptive current controller by using a conventional synchronous reference frame phase-locked loop (SRF-PLL). In this way, the current controller and synchronization part are merged into a single unit, which results in a simpler and more compact structure. The effectiveness of the proposed controller is verified using experimental results.


  1. Current control
  2. Distributed generation (DG) systems
  3. Phase-locked loop (PLL)
  4. Power converters
  5. Synchronization
  6. Three phase grid



Three-Phase Grid

Fig. 1. Power stage of a three-phase VSC with the proposed PLL-based controller and a harmonic/imbalance compensator.


PLL Based Controller

Fig. 2. Experimental results for the test 1.

Three Phase Grid

Fig. 3. Experimental results for the test 2.

Three Phase Grid

Fig. 4. Experimental results for the test 3.


In this letter, a PLL-based controller for grid-connected converters was proposed. This controller, which is realized by adding a positive feedback loop to the conventional SRFPLL, eliminates the need for a dedicated synchronization unit and, therefore, results in a more compact structure. To enhance the harmonic/imbalance rejection capability of the suggested controller, multiple complex integrators tuned at low-order disturbance frequencies is employed. To simplify the tuning procedure, a simple yet accurate linear model describing the frequency estimation dynamics of the proposed controller was was verified using some experimental results. The main contribution of this letter is not the proposed controller. It is actually demonstrating the possibility of making a frequency-adaptive controller from a standard PLL. The importance of this contribution will be more evident when we notice that there are a large number of advanced PLLs which can be explored for the controller design.


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