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Aiming at improving the efficiency of braking energy regeneration in hybrid power system of electric vehicle, hybrid power system (HPS) with battery, ultracapacitor and bi-directional DC/DC converter and normal strategy were studied. HPS was improved, which created three modes of regeneration. Piecewise control strategy of braking energy regeneration was proposed. In high-speed, middle-speed and low-speed each section, different modes of regeneration were carried out. According to voltage of ultracapacitor, speed of motor and so on, time of switchover between the sections was decided. Based on control of braking current of motor and time of switchover, smooth braking was achieved. Normal strategy and piecewise control strategy were experimentalized in different velocities on a miniature electric vehicle. The experimental results indicate that the efficiency of braking energy regeneration increases and smooth braking is achieved by the piecewise control strategy. [ABSTRACT FROM AUTHOR]