Experimental Comparison of Three Real-Time Optimization Strategies Applied to Renewable/FC-Based Hybrid Power Systems Based on Load-Following Control

Nicu Bizon,Mihai Oproescu

doi:10.3390/en11123537

Nicu Bizon, Mihai Oproescu

Open Access

https://doi.org/10.3390/en11123537

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Abstract

Besides three different real-time optimization strategies analyzed for the Renewable/Fuel Cell Hybrid Power Systems (REW/FC-HPS) based on load-following (LFW) control, a short but critical assessment of the Real-Time Optimization (RTO) strategies is presented in this paper. The advantage of power flow balance on the DC bus through the FC net power generated using the LFW control instead of using the batteries’ stack is highlighted in this study. As LFW control consequence, the battery operates in charge-sustained mode and many advantages can be exploited in practice such as: reducing the size of the battery and maintenance cost, canceling the monitoring condition of the battery state-of-charge etc. The optimization of three FC-HPSs topologies based on appropriate RTO strategy is performed here using indicators such as fuel economy, fuel consumption efficiency, and FC electrical efficiency. The challenging task to optimize operation of the FC-HPS under unknown profile of the load demand is approached using an optimization function based on linear mix of the FC net power and the fuel consumption through the weighting coefficients knet and kfuel. If optimum values are chosen, then a RTO switching strategy can improve even further the fuel economy over the entire range of load.

Highlights

In renewable energy Hybrid Power Systems (HPS) applications, the generation power is usually intermittent and variable, the load power is dynamic with the daily energy consumption, such as in Fuel Cell Hybrid Power Systems (FC-HPS), wind turbine farms, and solar arrays.The main objective for the FC-HPS [1,2,3,4] and other hybrid energy systems [5,6,7] is to efficiently operate these systems based on rule-based and optimization-based strategies proposed in the last years [8,9]
The global ES (GES)-based Real-Time Optimization (RTO) strategies will search the optimum of the optimization function (3a) for three sets of the k net and k f uel values: in the first situation, A, we have the following values for coefficients: knet = 0.5, kfuel = 0), for the second situation, B, we have the following values for coefficients: knet = 0.5, kfuel = 25, and for the third situation, C, the values for coefficients are: knet = 0.5, kfuel = 50
These scenarios have taken into account the power flow over the Direct Current (DC) bus: the load demand has been both, variable and constant, having or not having the power of RES

Summary

Introduction

The main objective for the FC-HPS [1,2,3,4] and other hybrid energy systems [5,6,7] is to efficiently operate these systems based on rule-based and optimization-based strategies proposed in the last years [8,9] As it is known, the deterministic rule-based strategy is already available in the market due to their reduced complexity in implementation, but this type of strategy cannot find the optimum solution [10], so the research interest has switched to optimization-based Real-Time Optimization (RTO) strategies, even if the complexity increases [1,11].

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Discussion

Conclusion