VOLTAGE STABILITY CONTROL OF DC MICROGRID FOR OFF-ROAD HYBRID ELECTRIC VEHICLES

For off-road hybrid electric vehicles (HEV) with special purpose, the powertrain is required to not only supply mechanical driving power to achieve high mobility, but also provide high-power electrical energy for mission payload, benefiting from coordination of engine, generator, motor, planetary gear set, battery, super capacitor, and DC/DC convertor. Essentially, powertrain of off-road HEV is a typical DC microgrid. However, stability of DC bus is faced with great challenges induced by random, fast, and intense ground drag disturbance in multimode driving conditions and stochastic electrical load by different mission profile as well. To solve this problem, a voltage stability control strategy for DC microgrid of off-road HEV is proposed in this paper. A stochastic control problem containing Ito's stochastic differential equations is established and a new multi-objective cost function considering bus voltage, engine response and fuel consumption is proposed. The stochastic optimal control problem is transformed into a deterministic optimal control problem using first-order moment and second-order moment, and the optimal power distribution is solved using a disturbance feedback control law. Compared with the rule-based strategy, this strategy can effectively suppress the sharp drop of bus voltage and reduce the impact of randomness on the system.