Three-phase PWM inverter providing an improved output sinusoidal waveform

In an inverter device comprising:

• an inverter main circuit including six bridge-connected switching elements which can be turned on and off in predetermined patterns so that a dc voltage supplied from an external source is converted to a three-phase ac approximately sinusoidal voltage and
• a three-phase PWM signal generating device connected to the inverter main circuit for generating switching pattern signals for turning on and off the switching elements in order to provide six kinds of switching patterns corresponding to six fundamental voltage vectors out of phase from one another by an electrical angle of 2.pi./6, respectively, and switching patterns corresponding to a zero vector corresponding to an "on" or "off" state of substantially all the switching elements so that the inverter main circuit generates an approximately sinusoidal output voltage waveform, the three-phase PWM signal generating device comprising
• phase command value classification means for classifying a phase command value .theta.*, pertaining to a voltage command value V*, into one of a plurality of unit regions, calculating a lead angle in the one unit region into which the phase command value is classified, and generating corresponding output information representative of the result of the classification and the lead angle, wherein the phase command value classification means obtains the plurality of unit regions by dividing an electrical angle of 2.pi. into a plurality of equal regions,
• switching pattern determining means supplied with the output information of the phase command value classification means for setting the switching patterns corresponding to two kinds of fundamental voltage vectors corresponding to the one unit region to which the phase command value is classified and the zero vector, the fundamental voltage vectors being out of phase from each other by an electrical angle of .pi./3, the switching pattern determining means further setting an output sequence of the set switching patterns, the switching pattern determining means forming the zero vector state at the times of the start and end of a section in which the calculated lead angle of the phase command value .theta.* advances .pi./3 and at the time of a change-over of the unit region so that the sum of the holding time of the zero vectors formed two times becomes approximately equal to the holding time of the other zero vector,
• holding time calculating means supplied with the output information of the phase command value classification means for calculating a holding time of each of the switching patterns corresponding to the two kinds of fundamental voltage vectors and the zero vector, based on the lead angle of the phase command value .theta.* belonging to the one unit region and the supplied voltage command value V*, and generating signals representative of the calculated holding times,
• timing means supplied with the signals representative of the calculated holding times and connected to the switching pattern determining means for holding a formation state of each set switching pattern during the holding time of each switching pattern calculated by the holding time calculating means, and
• unit region change-over determining means connected between the phase command value classification means and the switching pattern determining means for determining that the phase command value .theta.* has transferred from a unit region in the vicinity of one of the two kinds of fundamental voltage vectors.

In an inverter device comprising:

• an inverter main circuit including six bridge-connected switching elements which can be turned on and off in predetermined patterns so that a dc voltage supplied from and external source is converted to a three-phase ac approximately sinusoidal voltage and
• a three-phase PWM signal generating device connected to the inverter main circuit for generating switching pattern signals for turning on and off the switching elements in order to provide six kinds of switching patterns corresponding to six fundamental voltage vectors out of phase from one another by an electrical angle of 2.pi./6, respectively, and switching patterns corresponding to a zero vector corresponding to an "on" or "off" state of substantially all the switching elements so that the inverter main circuit generates an approximately sinusoidal output voltage waveform, the three-phase PWM signal generating device comprising
• switching pattern determining means for determining a holding time of each of the six kinds of switching patterns and an output sequence of the switching patterns, based on a command voltage vector including a supplied voltage command value V* and a supplied phase command value .theta.*, and
• command voltage vector substituting means for supplying to the switching pattern determining means a firs command voltage vector, instead of a command voltage vector received from an external source, when the command voltage value of the received command voltage vector exceeds a PWM control region where the fundamental voltage vector is a radius, the first command voltage vector being nearest to the limit of the PWM control region.

In an inverter device comprising:

• an inverter main circuit including six bridge-connected switching elements which can be turned on and off in predetermined patterns so that a dc voltage supplied from an external source is converted to a three-phase ac approximately sinusoidal voltage and
• a three-phase PWM signal generating device connected to the inverter main circuit for generating switching pattern signals for turning on and off the switching elements in order to provide six kinds of switching patterns corresponding to six fundamental voltage vectors out of phase from one another by an electrical angle of 2.pi./6, respectively, and switching patterns corresponding to a zero vector corresponding to an "on" or "off" state of substantially all the switching elements so that the inverter main circuit generates an approximately sinusoidal output voltage waveform, the three-phase PWM signal generating device comprising
• switching pattern determining means for determining a holding time of each of the six kinds of switching patterns and an output sequence of the switching patterns, based on a command voltage vector including a supplied voltage command value V* and a supplied phase command value .theta.*, and
• command voltage vector substituting means for supplying to the switching pattern determining means a first command voltage vector, instead of a command voltage vector received from an external source, the command voltage vector substituting means comprising
• determining means for determining to which one of first, second and third regions the received voltage command vector V* belongs, the first region being defined by the six kinds of fundamental voltage vectors into an orthohexagonal configuration, the second region extending from the first region vertically relative to each side of the first region, the third region extending in the direction of each fundamental voltage vector, and
• means for converting the received voltage command vector V* to a first command voltage vector nearest to a PWM control region when it is determined by the determining means that the received voltage command vector V* belongs to the second region, said means converting the received voltage command vector to the magnitude of the fundamental voltage vector when it is determined by the determining means that the received voltage command vector belongs to the third region, said means holding the received, voltage command vector when it is determined by the determining means that the received voltage command vector belongs to the first region.