Multilevel inverter (MLI) is one of the most efficient power converters which are especially suited for high power applications with reduced harmonics. MLI not only achieves high output power and is also used in renew...Multilevel inverter (MLI) is one of the most efficient power converters which are especially suited for high power applications with reduced harmonics. MLI not only achieves high output power and is also used in renewable energy sources such as photovoltaic, wind and fuel cells. Among various topologies of MLI, this paper mainly focuses on cascaded MLI with three unequal DC sources called asymmetric cascaded MLI which reduces the number of power switches. Various modulation techniques are also reviewed in literature [1]. In this paper we focus on sinusoidal (or) multicarrier pulse width modulation (SPWM) which improves the output voltage at lower modulation index for obtaining lower Total Harmonic Distortion (THD) level. The gating signal for the 13-level hybrid inverter using SPWM technique is generated using Field Programmable Gate Array (FPGA) processor. The proposed modulation technique results in reduced percentage of THD, but lower order harmonics are not eliminated. So a new technique called Selective Harmonic Elimination (SHE) is also implemented in order to reduce the lower order harmonics. The optimum switching angles are determined for obtaining minimum THD. The performance evaluation of the proposed PWM inverter is verified using an experimental model of 13-level cascaded hybrid MLI and compared with MATLAB/SIMULINK model.展开更多
A novel dual-wavelength fiber laser with asymmetric fiber Bragg grating(FBG) Fabry-Perot(FP) cavity is proposed and experimentally demonstrated. A couple of uniform FBGs are used as the cavity mirrors, and the third F...A novel dual-wavelength fiber laser with asymmetric fiber Bragg grating(FBG) Fabry-Perot(FP) cavity is proposed and experimentally demonstrated. A couple of uniform FBGs are used as the cavity mirrors, and the third FBG is used as intracavity wavelength selector by changing its operation temperature. Experimental results show that by adjusting the operation temperature of the intracavity wavelength selector, a tunable dual-wavelength laser emission can be achieved. The results demonstrate the new concept of dual-wavelength lasing with asymmetric FBG FP resonator and its technical feasibility.展开更多
文摘Multilevel inverter (MLI) is one of the most efficient power converters which are especially suited for high power applications with reduced harmonics. MLI not only achieves high output power and is also used in renewable energy sources such as photovoltaic, wind and fuel cells. Among various topologies of MLI, this paper mainly focuses on cascaded MLI with three unequal DC sources called asymmetric cascaded MLI which reduces the number of power switches. Various modulation techniques are also reviewed in literature [1]. In this paper we focus on sinusoidal (or) multicarrier pulse width modulation (SPWM) which improves the output voltage at lower modulation index for obtaining lower Total Harmonic Distortion (THD) level. The gating signal for the 13-level hybrid inverter using SPWM technique is generated using Field Programmable Gate Array (FPGA) processor. The proposed modulation technique results in reduced percentage of THD, but lower order harmonics are not eliminated. So a new technique called Selective Harmonic Elimination (SHE) is also implemented in order to reduce the lower order harmonics. The optimum switching angles are determined for obtaining minimum THD. The performance evaluation of the proposed PWM inverter is verified using an experimental model of 13-level cascaded hybrid MLI and compared with MATLAB/SIMULINK model.
基金supported by the National Natural Science Foundation of China(No.60777020)the Hubei Provincial Natural Science Foundation of China(No.2008CDB317)the Innovation Project of Hubei Provincial Department of Education of China(No.2012344/104892013043)
文摘A novel dual-wavelength fiber laser with asymmetric fiber Bragg grating(FBG) Fabry-Perot(FP) cavity is proposed and experimentally demonstrated. A couple of uniform FBGs are used as the cavity mirrors, and the third FBG is used as intracavity wavelength selector by changing its operation temperature. Experimental results show that by adjusting the operation temperature of the intracavity wavelength selector, a tunable dual-wavelength laser emission can be achieved. The results demonstrate the new concept of dual-wavelength lasing with asymmetric FBG FP resonator and its technical feasibility.
