Significant traction energy consumption for electrified train operation has posed a great challenge to metro systems, so seeking energy saving solutions is necessary. Among many energy-efficient operation methods, this paper proposes two combined energy saving solutions: applying Pontryagin's maximum principle for determining the optimal speed profile with fixed trip time in an aim at operating trains to track this optimal speed profile, and using active rectifiers replaces diode rectifiers in traction substations to recuperate regenerative braking energy as the electric trains track the optimal speed profile. Designing control for active rectifiers includes three control loops: the current control loop with sliding mode control, the voltage control loop, and phase-locked loop (PLL) enable energy to flow bi-directionally. When trains operate in braking phases, active rectifiers back the regenerative braking energy to utility source. Simulation results with data collected from metro line Cat Linh-Ha Dong, Viet Nam conducted on Matlab/Simulink have evaluated saving energy for the whole metro line is up to 11.96% compared with consumption energy without using any saving energy solutions.