A dual type inverter for increasing the capacity of a current source inverter with sinusoidal outputs is presented. Its main circuit configuration is very simple. Only one rectifier is used for supplying the dc power to two unit inverters, and the ac output terminals of each unit inverter are directly connected in parallel without a transformer. Since the dc power source is shared, the mean dc link voltage of each unit inverter must be equalized for current balancing. This can be achieved by supplying pulse-width modulated gate signals in the period of 120° and 180° in each unit inverter alternately. According to the experimental results obtained when a 1.5-kW induction motor is driven by a 2.5-kVA inverter, good current balance between the unit inverters is achieved. Both output voltage and current waveforms become almost sinusoidal. The 2-μF output terminal capacitor for overvoltage absorption and GTO switching frequency of about 1.2kHz are sufficient to produce sinusoidal output waveforms in the tested equipment. Since the harmonics contained in output voltage and current in the wide frequency range are decreasing even in the low GTO switching frequency, this strategy is suitable for increasing the capacity of a current source inverter with sinusoidal outputs.
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