High voltage adjustable speed drive systems offer significant advantages in many applications such as a fan, pump, or blower. In these applications, the adjustable speed drive systems achieves a higher level of system efficiency.
Usually, low voltage inverters with output transformer were used for a high voltage induction motor drive system. Recently, direct drive inverter system without output transformer has proposed and investigated. This inverter system is composed of single phase unit inverters and outputs multilevel voltages.
In this paper, pulse width modulation (PWM) technique suitable for high voltage direct drive inverter systems are discussed. At first, conventional multi-level PWM techniques based on the sub-harmonic method are shown and evaluated using time domain simulation. Next, new PWM method is proposed. This method has advantages that a modulation principle is very simple, distortion of the output voltage is very low, and well balanced switching losses among the unit inverters are achieved. Finally, simulation and experimental result are shown to illustrate the effectiveness of this method.
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