A current source inverter includes a controller, an input unit, a buffer unit, a modulating unit, and a commutator. The controller generates a switch control signal, an inverse switch control signal, a first pulse width modulation control signal, and a second pulse width modulation control signal. The input unit stores and transmits input power of a direct current power supply according to the first pulse width modulation control signal. The buffer unit is coupled to the input unit for receiving and transmitting the input power. The modulating unit generates and outputs a full-wave rectified sinusoidal current according to the second pulse width modulation control signal and the input power. The commutator converts the full-wave rectified sinusoidal current into an alternating current according to the switch control signal and the inverse switch control signal and outputs the alternating current to a load or a utility line.