# Improving the Energy Conversion Efficiency for Hydrokinetic Turbines Using MPPT Controller
## 4 Conclusions  
The main objective of the paper was to design a suitable power converter for a hydrokinetic turbine in order to extract the maximum power from the flowing water. Thus, a MPPT algorithm based on a perturb and observe method was implemented in a simulation program along with boost and buck converters for powering a considered load. A battery provided with BMS can be added when no power is required or the load varies.  
The novelty of the research is the implementation within the MPPT system of a DC/DC buck converter that controls the voltage applied to a certain load, compatible with a battery charging system. This improvement is necessary for ensuring a suitable voltage in case the system is provided with a battery that requires a certain constant voltage. In order to analyze and validate the MPPT algorithm, we chose the water velocity values so that the results could be compared to the experimental power curves of the hydrokinetic turbine. We noticed a good consistency between the two series of curves (shown in Figures 1 and 8), even though, for low water velocities, the algorithm overestimated the  
Figure 9: Rectifier DC voltage: Vdc (blue); boost converter output voltage: Vboost (green); buck converter output voltage: Vbuck (red).  
power output. For water velocities above 1 m/s, the algorithm predicted the power output with a precision of approximately 95%. The obtained results validate the simulated MPPT algorithm for a certain water velocity range, thus making it suitable for these kinds of applications.  
The output power supplied after the DC rectifier closely followed the maximum operating power point for a given resistance of the load, even if the voltage decreased due to reduced water velocity. Future research may consider improving the algorithm by implementing a battery connected to the load. The simulation model can be implemented as a general application for low-power hydrokinetic turbines. Depending on the specific application, the hardware solution can be easily designed on the basis of this algorithm to fit the load specifications. The critical input values are the parameters of the electric generator (including the voltage thresholds at certain rotational speeds) and the voltage required for the load, which can be set through the buck converter. Thus, the system will be able to obtain a suitable stabilized voltage level for most applications (battery charging systems, lightning, communication devices, etc.), making the small hydrokinetic turbines a viable solution for remote places where other renewable sources cannot be used.  
Conceptualization, R.-A.C. and I.V.; methodology, software, and formal analysis, I.V.; writing--review and editing, R.-A.C. and G.C.; literature review and investigation, G.C. and S.N.; data analysis and results interpretation, E.T. and C.D. All authors have read and agreed to the published version of the manuscript. This research received no external funding. This works was supported by the Romanian Ministry of Education and Research, CCCDI - UEFISCDI, project number PN-III-P1-1.2-PCCDL-2017-0391 - Smart Buildings Adaptable to the Climate Change Effects, project number PN-III-P2-2.1-PED-2019-1444 - Eco-hybrid Water Intake with Behavioral Barrier to Reduce the Impact on Fish Fauna and River Morphology, and by project number 30 PFE/2018 - Consolidation of the ICPE-CA Strategy in Supporting Advanced Research in the Field of Emerging Technologies in Electrical Engineering. The authors declare no conflict of interest.