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A new constant-frequency hysteresis current control in differential three-level grid-connected inverter is proposed. This method first sends the calculated hysteresis-band signal to the hysteresis comparator. By comparing the output PWM wave frequency with the given frequency, the amplified error signal through PI regulator then feedbacks to band-width signal to regulate slightly, which improves the current tracking, the output current waveform and the control precision. The new way not only remains the advantage of traditional hysteresis current control such as fast transient, good stability, but also makes the switch frequency constant, which optimizes the output filter design. The simulation results indicate that the new control is effective to stabilize the switch frequency and can promise the output current and the grid of the same phase, which ensures high quality power to the grid. The new control applied to the differential three-level photovoltaic grid-connected inverter is workable.