Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Patent
1988-07-12
1990-02-27
Salce, Patrick R.
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
363 41, 363 17, 318811, H02M 542, H02P 540
Patent
active
049051350
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an inverter apparatus which controls rotation speed of an electric motor by varying a frequency of a voltage supplied to an induction electric motor.
BACKGROUND ART
Generally, when an induction electric motor is driven by a convention inverter apparatus, a variable voltage--variable frequency control (hereinafter is referred to as VVVF control) is used. The VVVF control controls a magnetic flux of the motor so as to be always constant even when the output frequency of the inverter apparatus is varied. The VVVF control also controls fundamentally a ratio of a voltage applied to the motor and a frequency applied to the motor such that the ratio remains constant. Thus, the ratio V/F of an output voltage V and an output frequency F of the inverter apparatus is made constant.
An example of the conventional inverter apparatus is shown in FIG. 1. Numeral 1 designates a three phase or single phase power source, in this case a three phase power source. Numeral 2 designates a converter part (regular conversion part) of the inverter apparatus, and numeral 3 designates an inverter part (reverse conversion part). Numeral 4 designates the induction electric motor, which is three-phase coupled with inverter part 3. Numeral 12 is a PWM signal generating circuit which generates a pulse width modulating signal (hereinafter is referred to as PWM signal) of width proportional to an output frequency signal from an outside source. The PWM signal generated by PWM signal generating circuit 12 is transmitted to driver circuit 10 through a photo-coupler or a relay, and is input either as a base input signal or a gate input signal of a switching element such as power transistor, thyristor of inverter part 3 through driver circuit 10.
PWM signal generating circuit 12 has a memory and a microcomputer. An example of the relation of the PWM signal and the three-phase terminal voltage is shown in FIG. 2a and 2b. FIG. 2a shows a signal of inverter part 3 in a high output frequency, and FIG. 2b shows a signal of inverter part 3 in a low output frequency. The horizontal direction in FIG. 2a and FIG. 2b shows time and a vertical direction shows output values. In FIG. 2a, numeral 13 designates a triangular wave signal, and numerals 14, 15, 16 designate sinusoidal wave signals. The sinusoidal wave signals 14, 15, 16 have a phase difference of 120.degree. with respect to each other. A U-phase terminal voltage Vu is obtained by voltage comparison of sinusoidal wave signal 14 and triangular wave 13. A V-phase terminal voltage Vv is obtained by voltage comparison of sinusoidal wave signal 15, having a phase difference of 120.degree., to the sinusoidal wave signal 14. Finally, a W-phase terminal voltage Vw is obtained by voltage comparison of a sinusoidal wave signal 16, having phase difference of 120.degree., to the sinusoidal wave signal 15. When VVVF control is made, a ratio of wave height values of the sinusoidal wave signals 14, 15, 16 and a wave height value of the triangular wave signal 13 is changed by means of frequency. As a result, in high frequency (a state of FIG. 2a) the voltage applied to motor 4 is increased, and in low frequency (a state of FIG. 2b ) the voltage is reduced, such that the controlled ratio of the motor applying voltage and the frequency is usually constant.
By the above-mentioned principle, the PWM signal is generated by PWM signal generating circuit 12, and a switching timing of inverter part 3 is determined. In order to prevent a short circuit phenomenon by simultaneous trigger of the upper and lower elements which are coupled in series to the plural switching elements of inverter part 3, a short circuit preventing period td is set. The short circuit preventing period td is described in FIG. 6 of page 28 (834) of "MITSUBISHI DENKI GIHO" Vol. 58.No. 12.1984, and therefore the details are omitted.
A problem with the short circuit preventing period td is that it generates an error voltage corresponding to an output current from driver circuit 10 and distorts the out
REFERENCES:
patent: 4011489 (1977-03-01), Franz et al.
patent: 4698577 (1987-10-01), Seymour et al.
patent: 4767976 (1988-08-01), Mutoh et al.
patent: 4785225 (1988-11-01), Horie et al.
patent: 4800327 (1989-01-01), Fujioka et al.
M. Utaka et al,; "Noise-less Inverter Using BI-MOS Semiconductor Device"; pp. 25 (831)-pp. 29 (835); Mitsubishi Denki Giho, vol. 58, No. 12, published Dec. 25, 1984.
Seri Tutomu
Ueno Sachio
Unehara Shunsuke
Matsushita Electric - Industrial Co., Ltd.
Salce Patrick R.
Todd Voeltz Emanuel
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