Renewable energy utilization in the distribution network is increasing globally to tackle problems of traditional power production and transmission networks. By combining renewable energy sources with battery systems, the sustainability of the power system can be achieved while increasing its reliability. Purpose: nonlinear and unbalanced three-phase loads require specialized techniques to maintain their operation without compromising power system efficiency. Methods: a sustainable autonomous power supply system that utilizes a four-leg three-level inverter is proposed to operate such loads under difficult situations. Moreover, the operation of the integrated battery system is maintained by a fuzzy management controller that corresponds to the power mismatch between generation and demand. A user experience-based design has been followed in formulating the fuzzy system rules, while the output of the fuzzy management system represents the reference values for the battery current controller. This prompted the flexibility of the proposed management system for being implemented on different integrated units or under different operating conditions with minimal change. Furthermore, a combination of proportional resonant controllers and current controllers has been employed in regulating the load-connected inverter. This is to ensure the stability of the inverter and the achievement of the operational goals. Then, a special type of PWM generator has been used to generate the switching pattern of the proposed inverter's internal transistors. Results: the design has been tested in a simulation scenario under difficult conditions of generated power fluctuations and demand extreme nonlinearity and asymmetricity. However, the results indicated the effectiveness of the proposed inverter and management system in maintaining the stability and reliability of the power system.