جستجوی مقالات مرتبط با کلیدواژه "منابع dc متغیر" در نشریات گروه "برق"

Presence of triplen voltage harmonics and circuiting current in a delta-connected cascaded H-Bridge multi-level inverter causes extra power losses. In this paper, a low frequency optimization method is proposed to reduce triplen voltage harmonics in delta-connected cascade H-Bridge multilevel inverters. Using this method, in addition to reducing these harmonics, the total harmonic distortion (THD) is also maintained at optimum level and the requirements of standards such as EN50160, WG36-05 and IEC61000-3-6 are also satisfied.  In this method, using optimal minimization of total harmonic distortion (OMTHD), the optimal values of the switching angles and DC sources are obtained using the Particle Swarm Optimization (PSO) algorithm. The simulation and experimental results show the effectiveness of the proposed method in reducing triplen voltage harmonics and circuiting currents while keeping the THD at optimal levels.

In low switching frequency strategies, regulated DC sources along with the switching angles increase the system’s degrees of freedom to effectively mitigate or eliminate harmonics. Utilizing the variable DC sources increase the cost, losses and complexity of the system. This paper presents a new method for cascaded H-bridge multilevel inverters based on discrete variable DC source to reduce number of the regulated DC sources. In this paper, an optimization procedure for output voltage regulation is devised based on the discrete variable DC sources, which results in  effective reduction of harmonics and improvement of the output voltage quality. In the optimization method, the near optimum values of DC sources and switching angles are obtained using multi objective genetic algorithm. To verify the feasibility of the new solution, a laboratory prototype is implemented based on seven level cascaded H-bridge inverter with three cells in each phase. Simulation and experimental results validate the effectiveness of the proposed method based on the discrete variable DC sources in reduction of  harmonics and voltage regulation.

This paper proposes a generalized carrier-based pulse width modulation (GCB-PWM) technique suitable for multi-level back to back (BTB) converters. The objective of GCB-PWM technique is to produce a pulse pattern in such a way that the first non-eliminated harmonic contentof the output voltage is eliminated or reduced below its permitted value without increasing the switching frequency. This is achieved by fixing the amplitude modulation index in some special values but changing the intermediate dc link voltages instead; leading to salient advantages such as the total harmonic distortion (THD) improvement and output filter size reduction. The proposed GCB-PWM technique has been applied on a seven-level BTB cascaded H-bridge (CHB) system. Simulation results show the superiority of this technique over the conventional CB-PWM from the THD and filter size points of view.