A novel technology by using three-stage opamp design based on feedback capacitor for islanded mode microgrid stability control

This paper proposes a new method for controlling microgrids' frequency in islanded mode. The technique uses a multi-stage H-infinity (H∞) robust control method as a secondary controller to improve the performance of the droop control method. By utilizing the internal model of the H∞ control, the system can effectively regulate the frequency and reduce disturbance frequencies, leading to better power quality. The system's stability is enhanced by correctly adjusting two weighted parameters, ξ and μ, using the Harmony Search (HS) optimization algorithm. In addition, this work represents a new voltage compensation method for voltage regulators that drive a capacitive load ranging from pF-to-nF. The method relies on positive and negative feedback capacitors cooperating to ensure stability. Two circuits are suggested: Positive Feedback Compensation with Nulling Resistor (PFCNR) and Nested Miller Compensation Nulling Resistor (NMCNR). Designing the proposed circuit involves using Signal Flow Graph (SFG), Driving Point Impedance (DPI), and Analog Integrated Circuit Explorer (AICE) tools. Based on a set of design equations, the proposed algorithm is then used to determine the sizing of network components and transistor dimensions for the proposed circuits. The circuits are simulated and verified using 0.18 μm CMOS technology with a single power supply of 2 V. To prove the effectiveness of the proposed method, tests were conducted on an MG test system using MATLAB/Simulink. The controller was tested under different system disturbances, including changes in system loading, solar irradiation, wind power, and multiple signal disturbances. The proposed controller was compared with other control methods, such as droop, PI, and two-stage fuzzy logic-based PI controllers, using performance measures to evaluate the system's behavior. Stability analysis was also conducted using root locus, step response, singular value decomposition (SVD), and bode diagrams. The results show that the proposed control method is more effective in adjusting and controlling the MG frequency in islanded mode.