There are problems such as the large number of active components, unbalanced capacitor voltage, complex structure and low voltage gain in traditional multilevel inverters. Given these, this paper proposes a multilevel inverter that reduces the number of components and can be modularly expanded. The inverter is composed of a switched capacitor unit and two half bridges. It uses 1 DC power supply, 3 capacitors, and 13 switches to achieve 4 doubles voltage gain and a nine-level AC output voltage. Two half-bridges are used instead of the back-end H-bridge to convert the output voltage polarity. This can effectively reduce the total voltage stress of the switches. In the modular expansion structure of the proposed inverter, the step-by-step charging method of the capacitors further improves the voltage gain and the output level number. First, the working mode, modulation strategy, capacitance analysis, voltage stress calculation, and circuit parameter design of the proposed inverter are elaborated in detail. Then, it is compared with other similar multilevel inverters in recent literature. Finally, the feasibility of the proposed inverter and the correctness of the theoretical analysis are verified through simulation and experiment.