Study on Power-Split Hybrid Electric Propulsion Systems for Lightweight Helicopters

Abstract

In order to further study the possibility and potentiality of hybrid electric propulsion systems applied to helicopters, this paper aims at designing and analyzing power-split hybrid electric propulsion systems (PS-HEPSs) for the AC311 helicopter equipped with a diesel engine, and investigates the fuel consumption potential of PS-HEPSs. For helicopter operating conditions, the operating characteristics of power-split transmission systems are analyzed. It is found that the operating state (power split and power cycle) of PS-HEPSs depends only on the engine speed. Based on that, the paper proposes a three-parameter matching method of transmission ratios with an objective of maximum power-split speed range. Subsequently, by establishing a mathematical model of the PS-HEPSs for helicopters and adopting dynamic programming (DP) as the energy management, the fuel consumption and working points of power sources are calculated under the specific mission and also compared with the fuel economy of parallel hybrid electric propulsion systems (P-HEPSs). Results show that, by using the proposed method, the input power-split hybrid electric propulsion system and output power-split hybrid electric propulsion system (OPS-HEPS) have similar fuel consumption, but both consume less fuel than P-HEPSs. In terms of residual power, the OPS-HEPS still has 150 Kw left, because the generator can perform as a drive motor to provide torque. Although the power-split hybrid electric systems were first applied for automobiles, the comprehensive analysis shows that the PS-HEPSs are more suitable for helicopters because the constant speed of the output shaft reduces control complexity for PS-HEPSs.