Power converter for converting DC voltage into AC phase voltage having three levels of positive, zero and negative voltage

A power converter comprising:

• capacitors connected in series so as to divide a DC voltage;
• a DC/AC converter for converting said DC voltage charged on said capacitors into an AC output phase voltage having positive, zero and negative levels, which said output phase voltage is supplied to a load;
• and
• a modulation means for supplying said DC/AC converter with a signal so as to generate a sequence of alternating output pulses with interleaving zero-level pulses between a half cycle of a fundamental wave of said output phase voltage of said DC/AC converter and adjusting a width of only said output pulses having a same polarity as said fundamental wave of said output phase voltage depending upon a DC component of a difference between voltages on said capacitors.

A power converter comprising;

• capacitors connected in series so as to divide a DC voltage;
• and
• a DC/AC converter for converting said DC voltage charged on said capacitors into an AC output phase voltage having positive, zero and negative levels, which output phase voltage is supplied to a load;
• and
• a modulation means for supplying said DC/AC converter with a signal so as to generate a sequence of alternating output pulses with interleaving zero-level pulses between a half cycle of a fundamental wave of said output phase voltage of said DC/AC converter and adjusting a width of only said output pulses having a polarity opposite to said fundamental wave of said output phase voltage depending upon a DC component of a difference between a divided said DC voltage on said capacitors.

A power converter comprising:

• capacitors connected in series to divide a DC voltage;
• a DC/AC converter for converting direct current fed from said capacitors into an AC output phase voltage having positive, zero and negative levels;
• and
• a modulation means which divides a fundamental wave voltage instruction formed based on an amplitude instruction of a voltage and a frequency instruction output to said DC/AC converter into a positive-side voltage instruction for generating positive output pulses on a phase of said DC/AC converter and a negative-side voltage instruction for generating negative output pulses, and then forms a signal based on said positive-side and said negative-side voltage instructions to turn on or off switching elements that constitute said DC/AC converter, distributes distribution signals corresponding to DC components of a difference between voltages on said capacitors depending upon a polarity of said fundamental wave voltage instruction, and superposes said distribution signals on one of said positive-side voltage instruction and said negative-side voltage instruction.

An apparatus for controlling an electric car comprising:

• capacitors connected in series to divide a DC voltage;
• a DC/AC converter for converting direct current fed from said capacitors into an AC output phase voltage having positive, zero and negative levels;
• an AC motor driven by said output phase voltage from said DC/AC converter;
• and
• a modulation means which has a first modulation mode in which said DC/AC converter is supplied with a signal for generating a sequence of alternating output pulses with interleaving zero-level pulses in response to a voltage instruction and a frequency instruction fed to said DC/AC converter, a sequence of pulses corresponding to half a cycle of a fundamental wave of said output phase voltage of said DC/AC converter, and a second modulation mode in which said DC/AC converter is supplied with a signal for generating a sequence of output pulses different from a sequence of output pulses of said first modulation mode and adjusting a width of only either one of a positive and negative output pulse in a half cycle of said fundamental wave of said output phase voltage depending upon an imbalance of DC components between a divided said DC voltages in said first modulation mode and in said second modulation mode.

An apparatus for controlling an electric car comprising;

• capacitors connected in series to divide a DC voltage;
• a DC/AC converter for converting direct current fed from said capacitors into an AC output phase voltage having positive, zero and negative levels;
• an AC motor driven by said output phase voltage from said DC/AC converter;
• and
• a modulation means which has a first modulation mode in which said DC/AC converter is supplied with a signal for generating a sequence of alternating output pulses with interleaving zero-level pulses in response to a voltage instruction and a frequency instruction fed to said DC/AC converter, said sequence corresponding to half a cycle of a fundamental wave of said output phase voltage of said DC/AC converter, and a second modulation mode in which said DC/AC converter is supplied with a signal for generating a second sequence of output pulses different from said sequence of said first modulation mode and adjusting only a width of an output pulse which has a same polarity as said fundamental wave of said output phase voltage of said DC/AC converter depending upon a DC component of a difference between a divided said DC voltage.