Hybrid Electric Rice–Wheat Combine Harvesters for Low-Carbon and Intelligent Harvesting: A Review

Rice–wheat combine harvesters face coupled traction and material-processing loads whose variability complicates energy saving without reducing throughput or harvest quality. This review connects five perspectives: intelligent sensing, electrified actuation, hybrid powertrain architecture, field-condition prediction, and energy management. It examines interfaces under common quality and battery energy boundaries. Forward crop sensing, feed-rate monitoring, and component-load observation provide complementary information, while independent electric drives make drum, fan, and sieve settings more controllable. Series, parallel, and power-split architectures offer different compromises between controllability, conversion losses, packaging, and sustained-load performance. Direct evidence remains limited: one field prototype reported 19.5% lower fuel consumption than a conventional harvester, a study-specific result that does not establish a general saving range. Evidence from tractors and other vehicles supports transferable methods but cannot replace rice–wheat validation. A comparison matrix examines rule-based, instantaneous, optimal, predictive, and learning-based energy management. The framework couples fuel use and clean-grain throughput with loss, breakage, impurity, and state-of-charge constraints, and outlines life-cycle cost and carbon accounting. It is methodological rather than a new numerical assessment. The priorities are synchronized field duty cycles, uncertainty-aware coordination, thermal and fault validation, and comparisons across sites and seasons. The synthesis supports powertrain design and controller development for more energy-efficient and intelligent harvesting.