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It is clear that the harmonics in power systems have many negative impacts and therefore it is inevitable to reduce their amount to the accepted level and one of the interesting approach to reduce the harmonic distortion is to synchronize phase-shifted inverters operating in parallel. In this paper, a relatively modern technique for harmonic reduction employing synchronized phase-shifted three parallel PWM inverters with current-sharing reactors is analyzed. By using this method, the total harmonic distortion (THD) has been reduced significantly and the amount of reduction is directly proportional to the number of parallel phase-shifted inverters.

Inverters are widely used in many applications & the object of using the inverter is produce ac voltage with controllable magnitude & frequency. But the inverters where found in both the industrial motor drive industry & in the emerging distributed power generation industry, since these were essentially the only source of three phase inverters in the power range of interest. There are many types of multilevel inverters (MLI), but the cascaded multilevel inverter (CMLI) is most the favorite one for industrial applications. The three phase (CMLI) is used with optimization technique to suppress specific low-order harmonics or minimize total harmonic content & then improvement system efficiency .This technique of pulse width modulation (PWM) based on Walsh function harmonic elimination method. In this technique the harmonic amplitude of the inverter output voltage can be expressed as functions of switching angles. Thus, the switching angles are optimized by solving linear algebraic equations instead of solving nonlinear transcendental equations. This technique is suitable for higher level of three phase cascade multilevel inverter (CMLI) where other existing methods fail to compute the switching angles due to more computational burden. For the number of output voltage levels where multiple solutions exist, the solutions where produce least total harmonic distortion (THD) in the output voltage is chosen. As compared with previous work, the decrease in the THD can be reduced to (3%) in case of the proposed technique. In this paper, significant decrease in THD is obtained by solving linear algebraic equations for switching angles....

Electromagnetic Servo Relay Drive (ESRD) devices are small, simple and reliable devices. Special types of ESRD Utilizing Pulse Width Modulation (PWM) technique to input driving voltage are used in guidance and control systems. In this Paper a simulation, using MATLAB and Simulink were performed. To improve the rising time and time response of the mechanical armature angular position, the input voltage has been selected to do that. Two techniques have been proposed, first is the PID compensator and second is the reshaping / reforming the input pulse voltage. The effects on the different system parameters has been declared and discussed in addition to the comparison between the two used methods. Results show that the 2nd method is more effective and give an improvement in star sting and rising time by about 20% compared with 6% improvement in 1st method. The second method shows an increment in power consumption which lead in heat dissipation.