US 5,298,848 AGranted

Large capacity variable speed PWM spatial vector type sub-harmonic system for driving AC electric motor

AssigneeHitachi, Ltd.

InventorsShigeta Ueda, Takashi Ikimi, Mitsuyuki Hombu, Noboru Ogawa, Yorito Jifuku, Kenzo Kamiyama

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Abstract

A large capacity (1-2 MkVA) driving system for variable-speed-driving an AC motor by a power converter (inverter, converter) in which GTO (gate turn-off) thyristors are used as switching devices. In this system, high frequency GTO thyristors are connected in series, power converters are multiplexed, the AC motor is used in its plural phases, instantaneous spatial vector PWM (pulse width modulation) control is performed, vector control for the motor is performed, and a circuit for recovering snubber energy for GTO thyristors and a power factor adjusting circuit are provided. Thus, this driving system provides a torque ripple of 1% or less, speed response of 60 rad/sec or more, efficiency of 95% or more and a power factor of 98% or more.

Claims13

Dependent claims

A large capacity variable speed driving system for driving an AC motor by an inverter having a capacity of 2000 kVA or more including self-igniting elements for converting DC power into AC power, comprising:

an inverter system including a plurality of unit inverters connected in parallel in a multiplex manner;
and
a PWM (pulse width modulation) control device for controlling the output voltage from said inverter system;
wherein said self-igniting elements are GTO thyristors with a switching frequency of 500 Hz or more, and said PWM control device is a spatial vector type sub-harmonic system;
and
wherein said spatial vector type sub-harmonic system includes:
means for generating sine-wave three phase instantaneous voltage command signals V.sub.u *, V.sub.v * and V.sub.w *;
means for comparing the magnitudes of the three phase voltage command signals with one another to produce an intermediate value of the three phase voltage command signals;
means for adding a value V.sub.o, corresponding to half of the intermediate value, to the three phase instantaneous voltage command signals respectively to produce modulated wave signals V.sub.u **, V.sub.v ** and V.sub.w **;
means for generating a triangular wave signal e.sub.c at a frequency f.sub.c having a peak value corresponding to 1/4 of an input DC voltage E.sub.d to said triangular wave signal e.sub.c ;
means for generating a second carrier wave e.sub.c2 by subtracting the signal corresponding to 1/4 of said input DC voltage E.sub.d from said triangular wave signal e.sub.c ;
a first comparator for comparing said modulator wave signals V.sub.u **, V.sub.v ** and V.sub.w ** with said first carrier wave e.sub.c1 for each phase to form PWM signals for controlling a first unit converter;
and
a second comparator for comparing said modulated wave signals V.sub.u **, V.sub.v ** and V.sub.w ** with said second carrier wave e.sub.c2 for each phase to form PWM signals for controlling a second inverter unit.

11 more elements

A large capacity variable speed driving system for driving an AC motor by an inverter having a capacity of 2000 kVa of more including self-igniting elements for converting DC power into AC power, comprising:

an inverter system including a plurality of unit inverters connected in series in a multiplex manner;
and
a PWM (pulse width modulation) control device for controlling the output voltage from said inverter system;
wherein said self-igniting elements are GTO thyristors with a switching frequency of 500 Hz or more, and said PWM control device is a spatial vector type sub-harmonic system;
and
wherein said spatial vector type sub-harmonic system includes:
means for generating sine-wave three phase instantaneous voltage command signals V.sub.u *, V.sub.v *, and V.sub.w *;
means for comparing the magnitudes of the three phase voltage command signals with one another to produce an intermediate value of the three phase voltage command signals;
means for adding a value V.sub.o, corresponding to half of the intermediate value, to the three phase instantaneous voltage command signals respectively to produce modulated wave signals V.sub.u **, V.sub.v ** and V.sub.w **;
means for generating a triangular wave signal e.sub.c at a frequency f.sub.c having a peak value corresponding to 1/4 of an input DC voltage E.sub.d to said triangular wave signal e.sub.c ;
means for generating a second carrier wave e.sub.c2 by subtracting the signal corresponding to 1/4 of said input DC voltage E.sub.d from said triangular wave signal e.sub.c ;
a first comparator for comparing said modulated wave signals V.sub.u **, V.sub.v ** and V.sub.w ** with said first carrier wave e.sub.c1 for each phase to form PWM signals for controlling a first unit converter;
and
a second comparator for comparing said modulated wave signals V.sub.u **, V.sub.v ** and V.sub.w ** with said second carrier wave e.sub.c2 for each phase to form PWM signals for controlling a second inverter unit.

11 more elements

Dependencies are inferred from the claim text.