Four-switch three-phase inverter fed DTC system considering DC-link voltage imbalance

To compensate the voltage imbalance of the two split dc-link capacitors in a four-switch three-phase inverter fed direct torque control system, a modified space vector modulation (SVM) approach is proposed in this paper. The theory, design, and implementation of the modified SVM based DTC are discussed in detail, a new sector division method based on the real basic voltage vectors is introduced and a virtual zero vector synthesizing method is proposed. Experimental results verified the proposed SVM-DTC strategy for the four-switch three-phase inverter fed permanent magnet synchronous motor system, especially in low speed situation.