Maximising Regenerative Energy Return from Dynamo-Motor Traction Drives in Solar PV-Powered Electric Vehicles for Long-Haul Operation with Strong Stability

Abstract This thesis develops a design method for maximising the energy returned to the traction store of a solar photovoltaic (PV) powered electric vehicle by a dynamo-motor traction drive over a long-haul mission, while maintaining strong small-signal and large-signal stability of the on-board DC distribution network. The upper bound on that return is established first, by examining the widely repeated proposition of equal energy return against the first and second laws of thermodynamics. It is established analytically that a dynamo mechanically coupled to the traction load cannot, in isolation, return energy equal to the traction demand: the regenerative path is bounded by a round-trip efficiency of 74.8 per cent computed from the measured component chain, and it can act only upon the fraction of mission energy that is otherwise dissipated in braking. Equality is therefore admissible only when an external energy influx — here, the vehicle-integrated PV array — closes the deficit. A complete mathematical model is developed comprising longitudinal vehicle dynamics with grade, a dual-mode permanent-magnet machine model, a bidirectional power-conversion efficiency chain, a single-diode PV model with thermal derating, and a second-order equivalent-circuit battery model. A neutrality index is defined as the ratio of returned energy to traction energy, the recovery-maximising operating policy is derived, and the closed-form condition for unity index is obtained as the limiting case. Simulation of a 450 km hilly long-haul mission for a 3 500 kg vehicle with a 12.4 m² roof array in Abu Dhabi conditions yields a traction demand of 146.8 kWh, a regenerative return of 8.3 kWh and a solar harvest of 14.4 kWh, giving a neutrality index of 15.5 per cent. The equal-return condition is satisfied at a cruise speed of 10.8 km/h for the design array, or at 80 km/h only if the aperture area is increased beyond 91 m². Stability is assessed through an averaged small-signal state-space model of the 750 V DC link loaded by the traction inverter as a constant-power load. The undamped link is shown to lose stability at 64.3 kW, below the 95 kW peak traction rating; insertion of a virtual damping resistance of 0.62 Ω raises the critical power to 950 kW and secures a minimum damping ratio of 0.707, with a Lyapunov-based estimate of the region of attraction covering the full operating envelope. The recovery systems reduce specific energy consumption from 326.2 to 292.3 Wh/km and raise the arrival state of charge from 6.1 to 15.3 per cent, converting a mission that violates the depth-of-discharge limit into a feasible one. The work concludes that maximised recovery is a substantial and realisable design gain, whereas full energy neutrality is a bounded objective attainable only within a narrow envelope that is quantified here.