DC voltage balancing of flying converter cell active rectifier

In order to reduce input current distortions and improve power factor of a passive three-phase diode bridge rectifier, an active add-on-option circuitry (“Flying Converter Cell”) has been introduced recently. A novel voltage balancing concept for such an active three-phase rectifier which is based on the third harmonic injection principle using a Flying Converter Cell (FCC) is proposed in this paper. It is shown that the midpoint voltage of the FCC can advantageously be used for balancing of the DC capacitor voltages without disturbing the input currents. The proposed balancing concept can simply be added to the existing controller structure consisting of current controllers and a voltage controller. Using the proposed active balancing any losses of alternative passive balancing concepts (resistor networks) can be avoided which maximizes the system´s efficiency. The proposed concept is described in a simple mathematical manner, limitations of the concept are derived and basic operation is verified by simulation results. Measurement results taken from a laboratory prototype with an output power of 10kW finally demonstrate the good balancing characteristic of the proposed concept.