| Power Electronic-based Distribution Systems (PEDS) can provide excellent features such as load regulation, high power factor, and transient performance; especially in the large scale grids which are highly penetrated with the renewable energy resources, as well as innovative Power Electronic-based Components (PECs) such as Solid State Transformers (SSTs), Fault Isolation Devices (FIDs), machine drives, and inverters. Conversely, they are prone to exhibit negative impedance instabilities due to the regulated output voltage, high power factor and constant-power nature of the individual components in the system. Therefore, small-signal and large-signal stability assessments of the PEDS play a prominent role in the different stages of systems analyses such as preoperational (design), operational, and post-operational stages. Herein, various stability analysis techniques, along with their pros and cons, are described.;This work proposes to develop a novel "real time" stability analysis criterion and technique to assess small-signal stability of the PECs in the contemporary distribution systems. This will consist of a new small-signal stability criterion as well as appropriate technique to assess small-signal stability of the PECs based on the proposed criterion. The proposed criterion is developed based on d-q impedance measurement technique and Nyquist criterion. The advantages of the proposed criterion and technique include the capability to be developed for real-time applications, the simplicity of development on software and hardware, and the use of a powerful algorithm to address small-signal stability of the PEDS, etc. The primary contribution of this work is the real-time stability analysis methodology; more specifically, the capability of the proposed criterion and technique to be implemented in a real-time platform. The parallel perturbation of source and load is one of the key features of the proposed method that enables real-time capability. In addition, the proposed stability criterion, based on impedance measurement and Nyquist stability criterion, contributes higher accuracy in small-signal stability assessments of the systems by providing a complete Nyquist contour of the system's return-ration matrix. Ultimately, this yields lighter computational loads, faster computation times, and more accurate evaluation of the system's stability in a way that enables the assessment of the relative and absolute stability of the PEDS. Another advantage of the proposed technique is that it takes part of the system's nonlinearities into account by perturbing the systems with chirp signal and in a range of frequencies, instead of exclusively fundamental frequency.;Hardware development and experimental implementation also is presented in this work. In the experimental implementation section of the proposed work, an Impedance Measurement Unit (IMU) is developed via Power Hardware in the Loop (PHIL) experiment and measures source and load impedances in real-time. Subsequently, the proposed stability criterion is implemented on the real time digital simulator (RTDS) and by utilizing information from the developed IMU, small-signal stability of the test bed is investigated in real-time. |
