Electric power conversion systems – Current conversion – Having plural converters for single conversion
Patent
1998-12-17
2000-05-02
Han, Y. J.
Electric power conversion systems
Current conversion
Having plural converters for single conversion
318768, H02M 700
Patent
active
060580321
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a power conversion device for an electric vehicle utilizing a battery as a main power supply.
BACKGROUND ART
Power conversion devices for electric vehicles have hitherto required a high-voltage battery as a power supply.
FIG. 1 is a circuit diagram showing a conventional inverter for an electric vehicle. Inverter 502 converts the DC power from battery 503 to three-phase AC power by typically using semiconductor switches 601-606 as shown in FIG. 1 to drive AC motor 501. In this inverter 502, the maximum voltage that can be applied to AC motor 501 as interphase voltage is equal to the battery voltage due to the connections of semiconductor switches 601-606. A relatively inexpensive 200 V motor is typically used as AC motor 501. A DC voltage higher than 282 V (.apprxeq.200.times.2.sup.1/2), which is the amplitude of AC 200 V, is therefore required as the minimum input voltage of inverter 502 in order to obtain three-phase 200 V AC power as an AC output from inverter 502. A battery having a voltage of approximately 300 V is thus necessary to drive the 200-V motor.
To produce high voltage in a battery, however, 110 to 190 batteries each having cells of several volts each must be connected in series. A additionally, to charge a large number of batteries connected in series, a high-voltage direct-current voltage higher than that of the batteries must be produced by means of a charger. When charging a battery in which a large number of cells are connected in series, moreover, the voltages of each of the cells cannot be completely equalized due to the individual differences between the characteristics of each of the cells, and thereby causing variations in the charging conditions of each cell. The number of serial connections in the battery should therefore be reduced to a minimum to lower the charge voltage. Lowering the battery voltage however results in insufficient direct-current voltage for the AC motor.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a multiple pulse-width modulation power conversion device for variable-speed drive of a three-phase AC motor that accommodates the use of a low-voltage battery.
A first multiple pulse-width modulation power conversion device of this invention comprises: DC power supply or at least one battery cell, n power converters for converting the DC power of each of the batteries to single-phase AC power, and n residual capacitance detectors for detecting the residual capacitance of the batteries; and of the single-phase AC terminals within each unit, one of the single-phase AC terminals that is not connected to a single-phase terminal of another power converter is connected to a star connection, and the other single-phase AC terminal that is not connected is connected to a respective one of three input terminals of a three-phase AC motor; comprises control circuits for controlling said power converters such that AC outputs applied to single-phase AC terminals of the n power converters within each unit are of the same phase, and moreover, for effecting multiple pulse-width modulation such that AC outputs from the three units are separated by an electrical angle of 120.degree., and wave amplitude of AC voltage from the n power converters connected in series, based on the residual capacitance detected by each of the residual capacitance detectors.
When driving a three-phase AC motor at variable speeds using the power conversion device of the above-described construction, the output current and output voltage have a low-skew waveform because waveform control is effected by multiple pulse-width modulation, and in addition, power supply and regeneration are facilitated because conversion from DC to AC is a direct conversion. Further, this embodiment facilitates driving an AC motor by a low-voltage battery and allows incorporation of a battery charging capability to the power conversion device.
The invention thus enables use of voltage of a low-voltage battery, thereby increasing safety, improving
REFERENCES:
patent: 5040105 (1991-08-01), Dhyanchand et al.
patent: 5355296 (1994-10-01), Kuo et al.
Sawa Toshihiro
Tajima Eijiro
Yamanaka Katsutoshi
Han Y. J.
Kabushiki Kaisha Yaskawa Denki
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