Disturbance observer for dead-time compensation with variable gain and its stability analysis based on popov criterion

Dead-times are widely utilized for the inverters to prevent short-circuits. In motor drive applications, 6th-order torque pulsations caused by dead-times depend on rotational speeds of motors. A Disturbance OBserver (DOB) approach is effective for the dead-time compensation in low load operations. The performance of the DOB depends on the observer gains. Hence, if we use the conventional constant observer gains, the 6th-order torque pulsation cannot be suppressed effectively. In this paper, the DOB with the variable gain is proposed. Besides, its stability is analyzed based on the Popov criterion, because the proposed system contains the nonlinear system. In this paper, the ability to reduce the voltage errors by using the multi-level inverters is also introduced. In our analysis, the value of the voltage errors affects the stability. The validity of the proposed method is confirmed by our experimental results.