Implementation of parabolic current control for dual-carrier PWM

Hysteresis current control is a well-known nonlinear current control method for voltage source inverters. It can implement fast transient response and high control precision. A problem of hysteresis current control is that the system operates over a wide switching frequency range. This causes an increase in the switching stress of the active power devices and makes design of the output filter more complex. Parabolic current control solves this problem by employing a pair of parabolic carriers as the control band, achieving constant switching frequency while maintaining the fast transient response characteristic. Due to its high precision and fast speed, parabolic carrier control is an attractive nonlinear current control method especially suitable for voltage source inverters with applications such as uninterrupted power supply and active power filter. Dual-carrier pulse-width modulation is a popular modulation method widely utilized in voltage source inverters, due to the fact that it has lower output current ripple compared with conventional bipolar modulation. The conventional parabolic current controller generates two control states because it was originally proposed for the bipolar modulation method. As a result of the limited number of states for the original parabolic current control it cannot be directly used in dual-carrier pulse-width modulation controlled voltage source inverters. In order to solve this problem, a state machine based method is proposed in this paper, introducing a parabolic current control method to voltage source inverters that work under the operation of dual-carrier pulse-width modulation. The effectiveness of the proposed method is experimentally verified by the use of a full-bridge voltage source inverter prototype.