Optimized current reference generation for system-level harmonic mitigation in a diesel-electric ship using non-linear model predictive control

Abstract

Abstract-Non-linear optimal control using collocation and multiple shooting is investigated in this paper to generate the current reference signal for the lower level control of an active filter in a marine vessel with diesel-electric propulsion. The optimization objective is aimed at using the active filter for system-level minimization of Total Harmonics Distortion with the minimum rating of the active filter. The investigation of the different algorithms is oriented to the search of a solution that can offer a good compromise between accuracy and real-time implementation abilities. Results indicate that linear problem formulations are more suitable for real time implementation as they require less computational costs with minimal loss of flexibility. Non-linear problem formulations provide higher flexibility at the cost of higher computational efforts.

Handling system harmonic propagation in a diesel-electric ship with an active filter

“…However, in a system with dispersed loads and generators, the harmonic content can be further reduced if some kind of global optimisation is applied to the current reference. Optimisation for generating the active filter reference currents is discussed in [15] for the same topology as case 2 through applying Model Predictive Control (MPC). Case 2c and case 2d represent an initial attempt to optimise current references based on measurements from multiple loads.…”

“…[4]) in the most cost-efficient manner. For this purpose, optimisation methods can be applied both during design and operation phases as described in [15]. This paper has investigated how active filters can reduce harmonic content in diesel-electric ship power systems.…”

“…The control system objective is to provide a current i AF that is equal to the compensation current i comp,abc . The signal i comp,abc is normally chosen as equal to the harmonic current which the filter seeks to cancel, but it can also be selected in a more sophisticated way [15].…”

Management of harmonic propagation in a marine vessel by use of optimization

“…However, only test cases with symmetrical loads were presented in this study. When asymmetrical loads are present, and especially if load 1 is more distorted than load 2, the NMPC is expected to provide even better harmonic conditioning than local filtering due to the consideration of both loads [16,17].…”

Shaping the Current Waveform of an Active Filter for Optimized System Level Harmonic Conditioning

“…This paper, with references to (Skjong et al, 2015a) and (Skjong et al, 2015b), proposes such an approach based on optimization where the objective is to search for the optimum shape of the current waveform to be injected by an active filter to minimize the THD of the entire electrical system. To prove the concept, the optimization algorithm is implemented in the electrical system of a marine vessel (a discussion of harmonic mitigation using an active filter in a marine vessel's power distribution grid is given in (Rygg Aardal et al, 2015)).…”