The invention discloses a novel three-port Boost integrated converter for a photovoltaic energy storage system. The three-port Boost integrated converter only has one switching transistor. An inductorL1 works in a DCM mode, and an inductor L2 works in a CCM mode. By using a PWM+PFM hybrid modulation strategy and adjusting a duty cycle D and a switching frequency fs, PFM closed-loop control is applied to the photovoltaic array terminal voltage and PWM closed-loop control is applied to the load terminal voltage so as to control the photovoltaic array terminal voltage and the load terminal voltage. Compared with the main circuit of a traditional photovoltaic energy storage system which is formed by a cascaded Boost photovoltaic interface PWM converter and Boost energy storage interface PWM converter, the provided three-port Boost integrated converter removes one switching transistor and its driving module, improve system integration and efficiency, and reduce costs.