A variable switching frequency control method for active front end multilevel rectifier

Conventional back-to-back converters with input power factor correction are still the best solution for motor drive applications which are usually subjected to considerable load changes during their operation. Since converter components, especially input-side inductances are designed for nominal power rating, the rated input power factor and input current distortion aren't achievable in light loads. In this paper a control method is proposed to improve the input current distortion and input power factor in light loads. This is achieved by increasing the switching frequency according to the reduction in load. Since conduction and switching losses decrease in light loads, the overall losses by rising in switching frequency remain almost constant where the current is reducing. In this work, the total losses are considered proportional with the current. The effectiveness of the method is verified by simulations in which the input current distortion and power factor are improved using the proposed method at light loads compared to conventional fixed switching frequency control algorithms.