Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2000-10-16
2001-05-15
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
Reexamination Certificate
active
06233163
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an automatic balance adjusting device for an AC power supply and, more particularly, to an automatic balance adjusting device for an AC power supply that can measure the DC component of the AC power output, amplify and convert it into a current form, and send the signal through a photo coupler to a feedback control circuit to perform automatic compensation.
2. Description of Related Art
With reference to
FIG. 3
, a feedback control circuit (not shown but usually composed of a pulse width modulator (PWM)) is employed with the output circuit of an AC power supply to control the electrical communication among four power transistors Q
1
, Q
2
, Q
3
, Q
4
to generate an AC output at the output terminals. The feedback control circuit obtains a feedback signal from the AC output terminals to perform compensation and to ensure stable power output.
However, when the power transistors Q
1
, Q
2
, Q
3
, Q
4
and the feedback control circuit generate errors, the positive and negative half-cycle waves of the AC current output from the output terminals will have slight differences. In this situation, the waveforms of the positive and negative half-cycle waves are not the same. If the electrical load is inductive, the inductance in the load will be out of balance due to the integration of the voltage over time. This eventually will saturate the inductor.
Therefore, conventional AC power supplies often have different positive and negative half-cycle waveforms due to the errors in the power elements and the feedback control circuit. Providing an inductive load for a long time will saturate the inductance of the load. It is thus desirable to find a solution for such a problem.
SUMMARY OF THE INVENTION
A principal objective of the present invention is to provide an automatic balance adjusting device that can effectively detect the DC error component in the AC output signal of an AC power supply and send a converted error signal to a feedback control circuit to perform compensation.
The main technique to achieve the foregoing objective consists of providing an automatic balance adjusting device between the output terminals of the AC power supply and the feedback control circuit. The automatic balance adjusting device comprises a filter circuit, an integrator, a voltage/current conversion circuit and a separation control circuit. The filter circuit consists of a two-level filter and connects to the AC power output terminals of the AC power supply to detect the DC error component of the AC output signal. The integrator is made by using a resistor and a capacitor to provide negative feedback on an operational amplifier and is provided after the output terminals of the filter circuit to perform integrated amplification of the DC error. The voltage/current conversion circuit is composed of an operational amplifier with a resistor as a negative feedback so the output current varies with the input voltage and converts the amplified DC error in the voltage form to a current form. The separation control circuit is a photo coupler and is provided after the output terminals of the voltage/current conversion circuit so that the error signal in the current form can be separately sent back to the feedback control circuit to perform compensation.
The foregoing circuit design can effectively detect the DC component in the AC output waveform, amplify and convert it into a current form and send the error signal separately back to the feedback control circuit to compensate the difference between the positive and negative half-cycle waveforms.
Other features and advantages of the present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
REFERENCES:
patent: 4500837 (1985-02-01), Shuey et al.
patent: 4994767 (1991-02-01), Hawkes
patent: 5479090 (1995-12-01), Schultz
Lin Song-Yi
Shih Kuang-Chih
Berhane Adolf Deneke
Hedman & Costigan ,P.C.
Phoenixtex Power Co., Ltd.
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