Before rotating, fossil fuel-based, synchronous generators (SGs) are phased out, in line with renewable generation goals, grid-forming (GFM) inverters are expected to parallel SGs. Primary droop control allows GFM inverters to share power without communication; however, it is necessary to dispatch GFM inverters and/or SGs with the desired output power for better energy management (e.g., one GFM inverter needs to charge the battery due to a low state of charge). Therefore, this paper develops an analytic approach to dispatching GFM inverters and SGs with the desired output power by shifting the droop intercept up/down while maintaining the same frequency operating point for improved transient stability. This concept is demonstrated through a pure hardware setup with two off-the-shelf inverters and one diesel generator under an islanded microgrid, and we provide insight on the real-world implementation of the proposed concept.

Diesel hybrid power systems including inverter-based generation have faster and more stochastic dynamics than traditional systems. It is necessary to develop accurate models of the system components to ensure the stability of these systems and proper controller design. The parameters of the diesel generators in hybrid power systems, such as the inertia constant, are time-varying, requiring online parameter estimation techniques. This paper presents a simplified linear model developed to represent the frequency dynamics of the detailed diesel generator system and validated the model using a moving horizon estimation (MHE) approach. The proposed optimization-based MHE algorithm is employed to accurately provide an estimation of multiple parameters of a simplified diesel generator model. The proposed method extracts the parameters minimizing a cost function with a given set of constraints on the parameters. A non-intrusive square wave excitation signal generated by step changes in load is used to perturb the system with minimal impacts on power system operation. MHE estimates the parameters based on the power and frequency from the diesel generator system measured using the phase-locked loop (PLL) and provides reasonable estimates of unknown parameters. The estimated parameters are further verified by using them back in the simplified model and comparing them with the PLL measurements to represent the frequency dynamics of the diesel genset system.

Diesel generators are an integral component of remote islanded microgrids in rural Alaska. As inverter-based generation is integrated in these microgrids, adequate transient modeling will be necessary as dynamic and transient stability issues can arise with significant contributions of inverter-based generation. A complete transient model of a diesel generator includes models of the machine, exciter, governor, and any relays or other limiting components. Few studies compare the adequacy of various types of diesel generator governor or exciter models or include a volts/hertz (V/Hz) limiting functionality commonly found in diesel generators deployed in such remote islanded microgrids. This paper introduces and compares diesel generator models in response to two load steps against responses from the ACEP PSI lab 400 kVA diesel generator which represents a realistic diesel generator found in remote islanded Alaskan microgrids. A simplified governor model is introduced and compared to the traditional DEGOV governor model, and the functionality of a V/Hz limiter added to a DC4B exciter is demonstrated.