A new dead time compensation method for a pulsewidth modulation (PWM) inverter is proposed. In the PWM inverter, voltage distortion due to the dead time effects produces fifth and seventh harmonics in the phase currents of the stationary reference frame, and a sixth harmonic in the d-and q-axis currents of the synchronous reference frame, respectively. In this paper, the sixth harmonic of the integrator output of the synchronous d-axis proportional-integral (PI) current regulator is used to compensate the output voltage distortion due to the dead time effects, since the integrator output has ripple corresponding to six times the stator fundamental frequency. The proposed method can be easily implemented by feedforwardly adding compensation voltages to the output reference voltage of the synchronous PI current regulator. The proposed method, therefore, has some significant advantages such as simple implementation without additional hardware, easy mathematical computation, no offline experimental measurements, and application in both the steady state and the transient state. The validity of the proposed compensation algorithm is shown through several experiments.Index Terms-Dead time effects, integrator output of the synchronous d-axis proportional-integral (PI) current regulator, sixth harmonic, voltage distortion.
The authors report on an alignment layerless (AL) flexible liquid crystal (LC) display fabricated at ambient temperature through an imprinting process. One-dimensional microgrooves and two-dimensional arrays of microstructures embossed on plastic substrates provide the spontaneous alignment of the LC molecules and spacers for the uniform cell gap in a flexible LC display, respectively. It is found that the azimuthal anchoring energy, generated from the microgrooves, is on the order of 10−5J∕m2 which is strong enough to uniformly align the LC over large area. Our AL flexible LC display shows symmetric viewing characteristics and stable electro-optic properties under a bent environment.
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