This paper presents an energy-based modulation approach for a buck-boost inverter. Pulse Energy Modulation (PEM) is proposed as a new approach to generate inverter switching pulses based on the desired output energy. The energy demand is calculated from the output voltage and reference current and the modulation index of the inverter is calculated based on the instantaneous energy demand. The proposed method is applied to a single-stage buck-boost inverter. Detailed analyses of the inverter under discontinuous and continuous inductor current conduction modes are discussed. Simulation and experimental results show that PEM provides sinusoidal output current and robust control under large variations in the dc voltage and output current.