Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
2000-12-20
2001-11-27
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
C363S098000, C318S811000
Reexamination Certificate
active
06324085
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a power converter apparatus or an inverter apparatus for changing DC power into AC power. In addition, this invention relates to a method of controlling the drive of a polyphase AC-powered load via a power converter apparatus or an inverter apparatus.
2. Description of the Related Art
In general, an inverter apparatus or a power converter apparatus is provided between a DC power supply and an AC-powered load. The inverter apparatus receives DC power from the DC power supply. The inverter apparatus changes the DC power into AC power. The inverter apparatus feeds the AC power to the AC-powered load, and thereby drives the AC-powered load.
A typical power converter apparatus for a polyphase AC motor includes IGBT's (insulated gate bipolar transistors) as switching elements. Switching action of each of the IGBT's causes a power loss called a switching loss. As the frequency of switching rises, the switching loss increases. It is desirable to drive the polyphase AC motor while minimizing the switching losses caused by the IGBT's.
Japanese published unexamined patent application 59-139871 (application number 58-11678) discloses a pulse-width modulation system for the drive of a three-phase AC motor. In the system of Japanese application 59-139871, two-phase modulation is implemented. Specifically, the system includes three unit inverters for the three phases respectively. During every one sixth of a period (a cycle), one of the three unit inverters is controlled to fix a corresponding phase voltage while the two other unit inverters are controlled to conform the corresponding inter-phase voltages to sinusoids. Thus, a motor drive signal for one of the three phases is non-modulated while motor drive signals for the two other phases are modulated in accordance with the sinusoids. Selection of one from among the three unit inverters as corresponding to a non-modulated phase is designed to reduce the number of times of commutations per cycle, and hence to decrease commutation losses.
SUMMARY OF THE INVENTION
It is a first object of this invention to provide a power converter apparatus which can suppress the power loss caused by switching action of each switching element.
It is a second object of this invention to provide a method of controlling the drive of a polyphase AC-powered load which can suppress the power loss caused by switching action of each switching element.
A first aspect of this invention provides a power converter apparatus comprising an inverter main circuit including 1) switching elements responsive to switching control signals, and 2) means for applying phase voltages to a polyphase load via the switching elements; command value outputting means for outputting basic voltage command values for phases of the polyphase load respectively; command value converting means for converting the basic voltage command values outputted by the command value outputting means into final voltage command values respectively, wherein during a time interval for which at least two of the basic voltage command values are approximately equal to each other, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum; and control signal outputting means for subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values generated by the command value converting means to produce the switching control signals, and for outputting the switching control signals to the switching elements in the inverter main circuit.
A second aspect of this invention is based on the first aspect thereof, and provides a power converter apparatus wherein the command value converting means comprises means for equalizing at least one of the final voltage command values which is of a phase different from conversion object phases to a mean of inter-line voltages with the basic voltage command values of the conversion object phases.
A third aspect of this invention is based on the first aspect thereof, and provides a power converter apparatus wherein the polyphase load comprises a polyphase AC motor.
A fourth aspect of this invention is based on the third aspect thereof, and provides a power converter apparatus wherein the polyphase AC motor comprises a three-phase AC motor.
A fifth aspect of this invention provides a power converter apparatus comprising an inverter main circuit including 1) switching elements responsive to switching control signals, and 2) means for applying phase voltages to a polyphase load via the switching elements; command value outputting means for outputting basic voltage command values for phases of the polyphase load respectively; command value converting means for converting the basic voltage command values outputted by the command value outputting means into final voltage command values respectively, wherein a time interval for which at least two of the basic voltage command values are approximately equal to each other includes an alternation of first conversion time intervals and second conversion time intervals, wherein during each of the first conversion time intervals, the final voltage command values corresponding to said two of the basic voltage command values are equal to one of a maximum and a minimum, and wherein during each of the second conversion time intervals, only one of the final voltage command values corresponding to said two of the basic voltage command values is equal to one of the maximum and the minimum; and control signal outputting means for subjecting a carrier wave to pulse-width modulation responsive to the final voltage command values generated by the command value converting means to produce the switching control signals, and for outputting the switching control signals to the switching elements in the inverter main circuit.
A sixth aspect of this invention is based on the fifth aspect thereof, and provides a power converter apparatus wherein the command value converting means comprises means for setting a period of the alternation of the first conversion time intervals and the second conversion time intervals to an integer times a period of the carrier wave.
A seventh aspect of this invention is based on the fifth aspect thereof, and provides a power converter apparatus wherein during each of the second conversion time intervals, said only one of the final voltage command values corresponds to one of the basic voltage command values which is maximum in inter-line voltage with another of the basic voltage command value.
An eighth aspect of this invention is based on the fifth aspect thereof, and provides a power converter apparatus wherein the command value converting means comprises means for setting a length of the second conversion time intervals to a positive real number “n” times a length of the first conversion time intervals; means for, during each of the first conversion time intervals, subjecting at least one of the final voltage command values which is of a phase different from conversion object phases to level shift to maintain an inter-line voltage with the basic command voltage value of a conversion object phase in each of the second conversion time intervals; and means for, during each of the second conversion time intervals, subjecting one of the final voltage command values which is of a conversion object phase only for each of the first conversion time intervals to level shift to multiply an inter-line voltage with the basic voltage command value of a conversion object phase in each of the second conversion time intervals by (1+1
).
A ninth aspect of this invention is based on the eighth aspect thereof, and provides a power converter apparatus wherein the command value converting means comprises means for setting the positive real number “n” to 1.
A tenth aspect of this invention is based on the fifth aspect thereof, and provides a power converter apparatus wherein the command value converting means comprises means for increasing a lengt
Kimura Tomonori
Matsui Nobuyuki
Takeshita Takaharu
Denso Corporation
Law Office of David G. Posz
Nguyen Matthew
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