Seamless Transition of Microgrids Operation From Grid-Connected to Islanded Mode

Abstract

One of the main features of Microgrids is the ability to operate in both grid-connected mode and islanding mode. In each mode of operation, distributed energy resources (DERs) can be operated under grid-forming or grid-following control strategies. In grid-connected mode, DERs usually work under grid-following control strategy, while at least one of the DERs must operate in grid-forming strategy in islanding mode. A microgrid may experience remarkable fluctuations in voltage and current due to an unintentional islanding event. To achieve a smooth transition to islanding mode and mitigate disturbance effect, this paper proposes a control strategy includes a) a linear voltage controller with capacitor current feedback as an input to the voltage controller and output current feedforward as an input to current controller, and b) modified droop control to emulate the inertia response of a synchronous generator. The proposed controller can suppress voltage, current and frequency fluctuations and also guarantee a smooth transition. A small signal analysis of the proposed control strategy is developed to design its coefficients as well as the destabilizing effect of constant power load (CPL). Experimental results are provided to verify the effectiveness of the proposed control strategy.

Autonomous Control Strategy for Microgrid Operating Modes Smooth Transition

“…System details are listed in Table I. Also, the proposed control scheme with optimal parameters (hereafter "Proposed Control") is compared to the existing control strategy as in [5]- [8] (hereafter "Conventional Control") and the proposed control scheme with initialized parameters (hereafter "Initialized Parameters"). The conventional control strategy generally has voltage control mode for microgrid islanded operation and current control mode for grid-attached operation, and controller shall switch the mode when microgrid state transits correspondingly.…”

“…Most of the existing control approaches [5]- [8] implements the microgrid state transition by switching from CC-VSIs to VC-VSIs, and vice versa. For the comparative simulations in Section IV, the identical microgrid system and DGs are adopted.…”

“…Various techniques have been dedicated on microgrid transition control. Among the options, most existing transition control methodologies were implemented by changing voltage-controlled voltage source inverters (VC-VSIs) to current-controlled voltage source inverters (CC-VSIs), and vice versa [5]- [8]. The main drawback of this approach is that when fault occurs and the microgrid has to transit to islanded states unintentionally, protection devices (e.g.…”

Towards Grid of Microgrids: Seamless Transition between Grid-Connected and Islanded Modes of Operation

“…If the V-f magnitude exceeds the specified limits, the reference points obtained from the synchronous reference frame PLL are reverted to the original rated values 'ω O ' and 'E O '; thus ensuring a smooth transition between the GC and IS modes. Another modified droop-based linear voltage compensator for power converters forming the MG, has been proposed in [30]. Here, the scheme includes a) a voltage controller with capacitor current feedback input to the voltage controller and output current feedforward to input current control; b) a modified droop control that emulates the inertia response of a synchronous generator.…”

Resiliency‐oriented islanding of distribution network in the presence of charging stations for electric vehicles

“…Equations (8) and 9represent the maximum and minimum values of the active and reactive generated power of DGs. The voltage magnitude and angle limitations of each bus are specified in Equations (10) and (11). Equations (12) and (13) state that if a DG is selected as a master unit, magnitude and angle of the voltage of the corresponding bus are set at the set-point values.…”