In a renewable energy-based islanded microgrid system, frequency control is one of the major challenges. In general, frequency oscillations occur in islanded microgrids due to the stochastic nature of load and variable output power of distributed generating units (DGUs). In the presented research proposal, frequency oscillations are suppressed by implementing the proportional integral derivative (PID) controller-based control design strategy for an islanded microgrid. The modeling of the islanded microgrid is firstly presented in the form of a linearized transfer function. Further, the derived transfer function is approximated into its equivalent first-order plus dead time (FOPDT) form. The approximated FOPDT transfer function is obtained by employing the reaction curve method to calculate the parameters of the FOPDT transfer function. Furthermore, the desired frequency regulation is achieved for the manifested FOPDT transfer function by incorporating PID control design. For PID controller tuning, different rule-based methods are implemented. Additionally, comparative analysis is also performed to ensure the applicability of the comparatively better rule-based tuning method. The Wang–Chan–Juang (WCJ) method is found effective over other rule-based tuning methods. The efficacy of the WCJ method is proved in terms of transient response and frequency deviation. The tabulated data of tuning parameters, time domain specifications, and error indices along with responses are provided in support of the presented control strategy.

Frequency instability of an isolated microgrid (IMG) often arises due to load variations and uncertain power outputs of renewable sources. This contribution addresses the frequency instability issue by designing a Padula and Visioli (PV) tuned proportional-integral-derivative (PID) controller for IMG. The considered IMG model is novel due to the integration of eco-friendly generation sources, including a biogas turbine generator (BTG) and a biodiesel engine generator (BEG), along with other distributed generation units (DGUs) and energy storage devices (ESDs). In this contribution, mathematical modeling of considered units is derived as first-order model. Further, an overall transfer function of the IMG system is obtained using first-order transfer functions of IMG components and system dynamics. Thus, the obtained transfer function is then approximated into a first-order plus time delay (FOPTD) model to facilitate a simpler PID control design. PID controller parameters are computed using PV method for set point (SP) and load disturbance (LD) modes, keeping maximum sensitivity as a constraint. Various PID controller i.e. PID-PV_SP1.4, PID-PV_SP2.0, PID-PV_LD1.4, and PID-PV_LD2.0 is designed for SP and LD modes. The efficacy of PID control design is tested by analyzing its impact on frequency deviation and mitigation of error with acceptable transient response for SP and LD mode. A comparative study is also performed based on tabulated data featuring error indices, time domain indicators, control efforts, and frequency plots to validate PV method-based PID control designs for IMG. Moreover, the real-time simulator, i.e., OPAL-RT, is utilized to further validate the efficacy of the PID controller in frequency error mitigation of the considered IMG model.

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