Performance modeling of a hybrid Diesel generator-Battery hybrid system Central University of Technology Energy Postgraduate Conference 2013

Presentation outline Introduction System Layout Design variables Optimal operation control Operation strategies Conclusion

Introduction Small rural area electrification challenges: Reliable electrical power supply lacking, high cost of AC grid extension, rough topography. Diesel generator in rural electrification: Advantages: Low initial capital costs and generate electricity on demand. Disadvantages: Costs (operation fuel, maintenance running, replacement lifespan), Environmental impacts (noise and pollutions). Hybrid Diesel – Battery system: By optimally designing the hybrid generator-battery system and applying optimal operation control strategies, the overall running costs and well as the environmental impacts can be sensibly reduced.

This paper will propose an approach for optimal operation control of a hybrid Diesel generator - battery system with the aim of minimizing the operation cost while meeting the load energy requirements. The paper will be limited at the problem formulation and the development of the mathematical model for the performance of all the hybrid system’s components.

System Layout The proposed hybrid system is composed of a diesel generator, a battery storage system, an inverter, a charge controller as well as AC and DC loads. The hybrid system model is based on a description of current flow from the different sources, taking into account the losses and the impact of the operating decisions along the way up to the loads.

Design variables Diesel generator: The instantaneous output current from the DG depends on variables such as the type or the size of the DG used (X DG, Size, Type ). It can be expressed as: Battery storage system The instantaneous output current from the whole battery bank depends on variables such as the type or the size of the battery used (X Bat, Size, Type ), the number of battery strings in parallel X Bat. It can be expressed as: Inverter The size of the inverter X Inv is expressed in terms of its AC output power.

If X R, DC is the percentage of current from the DC bus (I DC ) redirected to the DC load, the input current to the inverter can be expresses as (1-X R, DC ). X R, DC is an operation variable. Transfer switch Its position (X S ) is an operation decision variable. If X S =0, all the AC load is supplied by the DG and the inverter is off. If X S =1, all the AC load is supplied by the DC bus through the inverter. Battery charger The size of the battery charger X BC in terms of its DC output power. The percentage (X R, AC ) of current from the DG (I DG ) redirected to the battery charger is:

Optimal operation control Objective function: The aim is to minimize the fuel consumption cost from the DG during the operation time. This can be expressed as: Where: N is the number of sampling intervals within the operation range or period of the system. a,b, c are coefficients. p is the price of the fuel. j is the j th sampling interval. I DG,j is the output current from the DG at j th sampling interval. Constraints: Load balance

Variable limits Operation limits Design limits Battery limits Operation strategies Diesel generator favourite: If the DG (CF) is between some preset values [CF X1 %, CF X2 %] and the battery state of charge (SOC) is between some preset values [SOC X1 %, SOC X2 %], then the DG is preferred. Battery system favourite: If the battery state of charge (SOC) is between some preset values [SOC Y1 %, SOC Y2 %] and the DG capacity factor (CF) is between some preset values [CF Y1 %, CF Y2 %], then the battery is preferred.

Conclusion The purpose of this paper was to propose an approach for optimal operation control of a hybrid Diesel generator - Battery system with the aim of meeting the load energy requirement while minimizing the operation costs all through the life of the system. The sizing optimization variables, operation decisions variables to be optimized at time t, as well as the constraints for the optimal sizing and operation control of the hybrid system have been described. The time independent operation strategies can be chosen by making a search through potential settings for the hybrid system optimal operation control. For further studies, the developed model can be integrated to the hybrid system’s total life cycling cost and then be used by any of the traditional (gradient-based methods) or modern (artificial intelligence) optimization algorithms to find the best solution for the system.