Low Power Energy Harvesting System for MISO Applications

Abstract

This thesis targets the study of the different architectures of modern energy harvesting systems especially the systems dealing with different energy sources. This work pro-poses an efficient energy harvesting system capable of extracting the energy from two different energy sources like a thermoelectric generator and a piezoelectric transducer cell while maintaining these sources regulated at their optimum operating voltage us-ing a dual-source maximum power point tracking unit. A wide range zero current switching circuit is also proposed to ensure discontinuous operation mode of the DC-DC converter. Moreover, the mathematical model of the output voltage and the input impedance is derived and verified with the simulation results. Chapter 1: This chapter starts with an introduction to the whole research then moving to the mo-tivation of this work. Also in this chapter the main objective and the main contribution of this research are demonstrated ending with the research organization. Chapter 2: This chapter presents the theoretical background and the literature review conducted by this research in the field of power management, especially in low-power energy harvesting systems. In this chapter different configurations of energy harvesting sys-tems are presented such as: single-input single-output systems (SISO), multiple-inputs multiple-outputs (MIMO). Moreover in this chapter, different implementations of the maximum power tracking (MPPT) unit and zero current switching (ZCS) circuits are all shown and compared with each other. Chapter 3: In this chapter, the proposed architecture of the multiple-inputs single-output (MISO) system is discussed showing all the technical details about the system blocks and specs. It starts with illustrating the different optimum operating points of the used energy sources. The mathematical model of the input impedance seen by each energy source is derived in this chapter and used to proposethe switch matrix and the control logic for the proposed MPPT unit. A frequency modulation technique with constant on-time is used to control inductor charging time using programmable dividers with the aid of a clock gating technique to reduce the power loss. Moreover in this chapter, a wide range zero current switching circuit (WR-ZCS) is presented in order to ensure discontinuousconduction mode (DCM) for the dual-input boost converter. At the end of this chapter, the coarse regulation unit including a low-power bandgap reference, continuous-time comparator and a voltage independent current source are all pre-sented. Chapter 4: In this chapter, all simulation results for the system operation are presented. MPPT transient response at different cases to show that the system always toggles between two sub-states around the optimal state at steady-state achieving maximum power to be delivered to the load. Moreover, the proposed technique for the wide-range zero-current switching circuit is presented to ensure the proper off-time for both energy sources with a good resolution. In the end of this chapter, the coarse-regulation scheme is presented to show thesystem robustness and long-operational time.Regulation is ensured under different sources and load conditions once system reached steady-state.

Chapter 5: In this chapter, the mathematical model of the converter output voltage is presented. The presented model is verified with simulation results at different operating condi-tions such as: different harvesters’ conditions with different resistances and at differ-ent load values. The model results are very close to the simulation results. Chapter 6: This chapter concludes the thesis, summarizing the research work and out-puts.Moreover, further enhancements to this work are suggested.