A new topology and control scheme for 4WD HEV using a DFIM with a reduced size converter-inverter

In a stand alone system such as a hybrid electrical vehicle (HEV) and an electrical propulsion ship, an electric energy is transferred from a generator to a target motor via a converter-inverter set to control the motor torque or speed. In this case, whole power is handled by the converter-inverter system, and the power rating of the converter tends to be large. This work proposes a topology and a control scheme for a 4WD HEV system using a doubly fed induction motor (DFIM) which is driven by an internal combustion engine. The control aim is to produce a variable voltage variable frequency (VVVF) voltage from the stator terminal of the DFIM by injecting a slip frequency into the rotor winding through an inverter. In other words, the source voltage for target motor is not synthesized by an inverter after making a DC-link. Instead, the generator stator terminal directly provides a VVVF voltage to the motor. The inverter supplies current having slip frequency to the rotor via slip ring. Since the DFIG output voltage and frequency are controlled by the rotor current, the inverter power rating can be reduced significantly, when it is compared with the generated power. In this work, it is shown that with the proposed topology the power rating of a converter-inverter could be reduced to the 1/4 of the original converter-inverter system.