Inverter for changing direct current to alternating current

Details Inverter for changing direct current to alternating current Inverter for changing direct current to alternating current

2003-01-24

2004-09-28

Sherry, Michael (Department: 2838)

Electric power conversion systems

Current conversion

With condition responsive means to control the output...

C363S017000

Reexamination Certificate

active

06798676

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DC to AC inverter, and particularly to an inverter, with which the direct current (DC) can be changed to the alternating current (AC) by means of a switch circuit and a transformer so as to simplify the circuit structure and enhance the reliability for saving the cost.
2. Description of Related Art
A conventional circuit for inverting the direct current to the alternating current includes a voltage rise circuit (
10
′), a bridge type rectifier (
20
′), a filtering capacitor (C
2
′), two pulse width modulators (PWM
1
, PWM
2
), a bridge type switch circuit (
10
) and a control-drive circuit (
40
). The voltage rise circuit (
10
′) has switch transistors (Q
1
, Q
2
) and a transformer (T
1
) to form a push-pull type voltage rise circuit (
10
′) with a DC input positive end being connected to a central node of the transformer (T
1
). The transformer (T
1
) further connects with a DC negative input end via the switch transistors (Q
1
, Q
2
) Under the control of the pulse width modulator (PWM
1
), the input direct current can obtain a voltage rise via the transformer (T
1
) and the switch transistors (Q
1
, Q
2
) and output with a high voltage from the secondary side of the transformer (T
1
). The high voltage current is rectified with the bridge type rectifier (
20
′), which has four rectifying diodes (D
1
-D
4
), and filtered with the filtering capacitor (C
2
′) so as to obtain a stable direct current with a high voltage. The high voltage direct current is led to the bridge type circuit (
10
), which is composed of four switch transistors (Q
3
-Q
6
), and can produce a pulse width modularized low frequency (═Hz or 60 Hz) waves by means of the pulse width modulator (PWM
2
) so as to be output with alternating current via the control-drive circuit (
40
). However, the pulse width modulators (PWM
1
, PWM
2
) can be operated with low frequency only so that it is possible for the pulse width modulators (PWM
1
, PWM
2
) to control the output voltage of the alternating current only and the output wave is incapable of being controlled. Thus, the output wave is a modified sine wave as shown in
FIG. 2
instead of a pure sine wave.
Next, another conventional DC to AC inverter is illustrated in FIG.
3
and the second conventional inverter has been added an energy inductor L
1
and has a wave generator (
30
) in the control-drive circuit (
40
) so as to produce a low distorted sine wave for the pulse width modulator (PWM
2
) being capable of performing comparison. The output of the pulse width modulator (PWM
2
) can be shifted to signals required by the switch transistors (Q
3
-Q
6
) via the control-drive circuit (
40
) and the signals drive the bridge type switch circuit (
10
), which is composed of the four switch transistors (Q
3
-Q
6
), so that the switches can be operated with a change between a high frequency and a low frequency. The output with a low distorted sine wave can be obtained after being energy saved and filtered with the energy storage inductor L
1
. However, the second conventional inverter has to be provided with a transformer, two stages of switch circuits (
10
′)(a push-pull type voltage rise circuit composed of switch transistors (Q
1
, Q
2
) and a bridge switch circuit (
10
) composed of four switch transistors (Q
3
-Q
6
)) and a rectifying and filtering circuit (a bridge type rectifier (
20
′) composed of rectifying diodes (D
1
-D
4
) and a filtering capacitor (C
2
′)). The preceding parts need large power to result in large stress and it is easy to become out of order. Further, the preceding circuits need a lot of components so that the inverter is high in cost.
In addition, the preceding conventional inverter at the output end thereof is a switch circuit (
10
) composed of four switch transistors (Q
3
-Q
6
) and the switch circuit (
10
) is operated under a state of high voltage. Once the output is overload or short circuit, the four switch transistors (Q
3
-Q
6
) are easy to be burned due to extra large instantaneous power. As a result, the circuit is hard to be protected with high production cost and unfavorable reliability.
SUMMARY OF THE INVENTION
An object of the present invention is provide a DC to AC inverter, which includes a bridge type switch circuit, a transformer, an integrated circuit, a pulse width modulator, a wave generator and a control-drive circuit. The switch circuit is connected to a direct current power source and has two alternating current ends with one of the alternating current ends connecting with an energy storage inductor in series and then connecting with an input end of the transformer and the other input end of the transformer being connected to the other alternating current end. The current waves at both of the alternating current ends are detected and the waves are integrated and sent to a feedback end of the pulse width modulator. The wave generator produces half period of sine waves for a reference potential end and low frequency (═Hz or 60 Hz) square waves for the control-drive circuit operating the pulse width modulator and the square waves and sending control signals to the switch circuit. The direct current can be converted to the alternating current by way of a switch circuit and a transformer such that the circuit structure can be simplified and the reliability can be enhanced with economical cost.


REFERENCES:
patent: 5519598 (1996-05-01), Sakai et al.
patent: 5625539 (1997-04-01), Nakata et al.
patent: 5696670 (1997-12-01), Roederer et al.

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