Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Patent
1984-02-17
1986-11-25
Salce, Patrick R.
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
323207, H02P 1324, H02J 318
Patent
active
046252720
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a power-supply apparatus employing a converter (PWM converter) which is controlled by pulse width modulation, and particularly to a power-supply apparatus which is capable of controlling a d-c voltage to a desired value when the converter is subjected to the regenerative operation.
BACKGROUND ART
A PWM converter has been well known, which is made up of Graetz-connected transistors or self-extinguishing elements such as gate turn-off thyristors. The magnitude and phase of an input current can be controlled if the a-c input terminals of the PWM converter are connected to an a-c power supply via reactors, and if the magnitude and phase of an a-c input voltage are instantaneously controlled with the a-c power supply voltage as a reference. It is therefore possible to arbitrarily control the effective electric power which is supplied from the a-c power supply to the PWM converter. For instance, Japanese Patent Laid-Open No. 94583/1980 proposes an apparatus and a method for this purpose. Since the effective power is converted by the PWM converter into d-c power, it is possible to control the d-c output voltage (current) to any desired value.
Feedback diodes have been connected in parallel, but in the opposite direction, with the self-extinguishing elements which constitute the PWM converter. To control the PWM converter by pulse width modulation, the d-c output voltage must be greater than diode-rectified voltage of the a-c power supply voltage. This is because, if the d-c voltage becomes smaller than the diode-rectified voltage the a-c power supply voltage, the d-c power is supplied through the feedback diodes of the PWM converter to hinder the pulse width modulation control.
Further, when the load of the PWM converter is subjected to a regenerative operation, the PWM converter will also be subjected to the regenerative operation. In this case, the d-c voltage is likely to become considerably greater than the diode-rectified voltage.
Depending upon the load connected to the d-c side of the PWM converter, on the other hand, the d-c voltage must often be equal to, or smaller than, the diode-rectified voltage of the a-c power supply voltage. When the load is an inverter or a chopper, this is necessary to prevent the elements from breaking.
Thus, when the PWM converter is used, it is strongly recommended to control the d-c voltage to make it equal to the diode-rectified voltage of the a-c power supply voltage.
DISCLOSURE OF INVENTION
The object of the present invention is to provide a power-supply apparatus which is capable of controlling the voltage on the d-c side of the PWM converter to become smaller than the diode-rectified voltage of the a-c power supply voltage. When the deviation between an instructed value and a detected value of the d-c voltage indicates that the detected value is greater than the instructed value, the power-supply apparatus is operated with a lagging power factor. Therefore, the a-c voltage input to the PWM converter is made smaller than the a-c power supply voltage, thereby to decrease the voltage on the d-c side.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 a diagram showing the setup according to an embodiment of the present invention;
FIG. 2 is a detailed circuit diagram of a PWM converter;
FIG. 3 is a diagram showing characteristics of a phase shifter of FIG. 1;
FIG. 4 is a diagram which schematically shows the setup to explain the principle of the present invention;
FIGS. 5(a) and (b) and 6(a) and (b) are vector diagrams for explaining the principle of the present invention;
FIG. 7 is a diagram showing the setup according to another embodiment of the present invention;
FIG. 8 is a vector diagram for explaining the operation of FIG. 7;
FIG. 9 is a diagram showing characteristics of a phase shifter of FIG. 7;
FIGS. 10 and 11 are diagrams showing setups according to further embodiments; and
FIG. 12 is a diagram showing characteristics of a reactive current instruction circuit in the embodiment of FIG. 11.
BEST MODE FOR CARRYING OUT
REFERENCES:
patent: 4449176 (1984-05-01), Turnbull
Kubota Yuzuru
Okuyama Toshiaki
Hitachi , Ltd.
Rebsch D. L.
Salce Patrick R.
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