Modified staircase modulation with low input current distortion for multicell converters
ABSTRACT Cascaded H bridge multilevel inverters are traditionally controlled using phase shifted PWM. This method allows an even power distribution among the different cells of the converter, which enables input current harmonic cancellations due to the isolation multipulse transformer and rectifier system. For high power applications a selective harmonic elimination based method, also known as staircase modulation, has been proposed. This method is devised to reduce switching losses to a minimum, improving the efficiency of the converter. The switching angles are calculated to eliminate low order harmonics at the output voltage. However, this method does not provide even power distribution among the cells, avoiding the input current harmonic cancellation. This work proposes a redistribution of the switching angles between the cells, maintaining the overall switching pattern of the staircase modulation. The methods maintains the harmonic elimination characteristic at the output voltage, while improving the power distribution and consequently the input current harmonic performance. Mathematical analysis and simulation results are presented to support the strategy.
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ABSTRACT: A new approach to medium-voltage variable-frequency static AC motor drives offers improvements in power quality. Harmonic current injection into the power lines is below the most severe requirements of IEEE Standard 519-1992. The power factor of this new type of drive exceeds 94% at full load and is above 90% at 10% load. Motor voltage and current waveforms are improved so that torque pulsations are reduced. Peak voltage stress on motor insulation does not exceed peak input line voltage, and no zero sequence voltage is imposed. Drive efficiency exceeds 96%. This paper describes the new approach and some of the results achievedIEEE Transactions on Industry Applications 02/1997; · 1.67 Impact Factor
Conference Proceeding: A practical harmonics elimination method for multilevel inverters[show abstract] [hide abstract]
ABSTRACT: This paper proposes a new practical harmonics elimination method for multilevel inverters. Unlike other methods published before, the proposed method does not need to solve high order polynomials. Only four simple equations and minimum calculation time are needed.Industry Applications Conference, 2005. Fourtieth IAS Annual Meeting. Conference Record of the 2005; 11/2005
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ABSTRACT: This paper presents a new multilevel pulse width-modulation (PWM) inverter scheme for the use of stand-alone photovoltaic systems. It consists of a PWM inverter, an assembly of LEVEL inverters, generating staircase output voltages, and cascaded transformers. To produce high-quality output voltage waves, it synthesizes a large number of output voltage levels using cascaded transformers, which have a series-connected secondary. By a suitable selection of the secondary turn-ratio of the transformer, the amplitude of an output voltage appears at the rate of an integer to an input dc source. Operational principles and analysis are illustrated in depth. The validity of the proposed system is verified through computer-aided simulations and experimental results using prototypes generating output voltages of an 11 level and a 29 level, respectively, and their results are compared with conventional counterparts.IEEE Transactions on Energy Conversion 01/2006; · 2.43 Impact Factor