Power converting apparatus including half-bridge inverters connected between positive and negative terminals of a DC power supply

A power converting apparatus comprising:

• three sets of half-bridge inverters connected between positive and negative terminals of a DC power supply, each set of half-bridge inverters including two series-connected switching devices;
• plural sets of single-phase inverters connected in series with individual AC output lines of said three sets of half-bridge inverters, each set of single-phase inverters including a plurality of series-connected single-phase inverters;
• first connecting means for connecting the output terminals of said individual single-phase inverters to individual phases of a three-phase power system;
• and
• second connecting means for disconnecting said plurality of single-phase inverters of one phase from the relevant phase and connecting the same number of single-phase inverters to the AC output lines of the other two phases, and connecting the individual AC output lines of the two phases to two phases of a three-phase power system other than one phase thereof which is grounded, wherein
• said power converting apparatus is configured to permit switching from said first connecting means to said second connecting means, each of said half-bridge inverters is caused to output voltage pulses of which frequency is same to that of a system voltage, and said individual single-phase inverters are controlled by PWM control operation to make up for a voltage insufficiency from the system voltage.

A power converting apparatus comprising:

• plural sets of half-bridge inverters connected between positive and negative terminals of a DC power supply, each set of half-bridge inverters including two series-connected switching devices;
• and
• single-phase inverters connected in series with individual AC output lines of said plural sets of half-bridge inverters, wherein,
• each of said half-bridge inverters is caused to output one pulse of voltage and is controlled by PWM control operation in regions of both edges of the pulse every half cycle of a system voltage, and said individual single-phase inverters are controlled by PWM control operation to make up for a voltage insufficiency from the system voltage, and
• each of said half-bridge inverters is controlled by the PWM control operation during each period in the vicinity of a point at which the system voltage is zero and is caused to output the one pulse of voltage having a pulsewidth corresponding to each period in other than the period of the PWM control operation every half cycle of the system voltage.