Electricity: single generator systems – Automatic control of generator or driving means – Voltage of generator or circuit supplied
Patent
1990-11-21
1991-07-30
Wong, Peter S.
Electricity: single generator systems
Automatic control of generator or driving means
Voltage of generator or circuit supplied
363 37, 363 41, 363 98, 363132, H02P 948, H02J 714
Patent
active
050362682
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns a procedure and apparatus for producing an a.c. voltage.
In particular in small combustion engine-driven generators producing a sinusoidal a.c. voltage, it is difficult to manage simultaneously both constant frequency and amplitude under changing load conditions because the frequency, and often also amplitude, are determined by speed of rotation exclusively. The speed is controlled using a centrifugal regulator or another mechanical governor, which in order to react requires a fairly large change in speed of rotation. Moreover, exact attainment of the correct frequency often requires separate measurement and continuous monitoring. Achieving a good sinusoidal waveform requires shaping the generator windings and air gaps in a way deviating from a design which is required to obtain maximum output power. As a result, the bulk of the generator increases and the weight increases in relation to the power output achieved.
SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the drawbacks mentioned above. The procedure of the invention for producing an a.c. voltage is mainly characterized in that the a.c. voltage is formed via inversion from a d.c. voltage produced by means of a generator, that the d.c. voltage is measured and stabilized, and that the frequency of the a.c. voltage is generated with an oscillator. Since the frequency of the a.c. voltage is thus produced with a separate oscillator, a constant frequency independent of load and the speed of rotation of the generator is obtained. As the amplitude of the a.c. voltage is at the same time produced separately independent of frequency, stabilizing the amplitude becomes easier.
An advantageous embodiment of the procedure of the invention is characterized in that the d.c. voltage is stabilized by controlling the magnetization of the generator.
An advantageous embodiment of a procedure according to the invention is also characterized in that the oscillator uses a crystal for frequency stabilization.
An advantageous embodiment of the procedure of the invention is also characterized in that the a.c. voltage is filtered in conjunction with the a.c. conversion.
The apparatus implementing the procedure of the invention is characterized in that the apparatus comprises an inverter containing a control unit for producing the a.c. voltage via inversion from a d.c. voltage, a generator unit for producing a d.c. voltage by means of a generator, a d.c. voltage control unit for measuring and stabilizing the d.c. voltage obtained from the generator unit, and an oscillator unit in the control unit of the inverter for determining the frequency of the a.c. voltage.
An advantageous embodiment of the apparatus implementing the procedure of the invention is characterized in that the magnetization of the generator can be controlled by means of the magnetizing winding so as to stabilize the output voltage of the generator unit.
An advantageous embodiment of the apparatus implementing the procedure of the invention is also characterized in that the d.c. voltage control unit contains an operational amplifier for comparing the d.c. voltage produced in the generator unit to a reference voltage, transistors which together with the operational amplifier, amplify the difference between the d.c. voltage and the reference voltage, and a diode for excess voltage protection.
An advantageous embodiment of the apparatus implementing the procedure of the invention is also characterized in that the power stage of the inverter comprises semiconductor switches for producing an a.c. voltage from the d.c. voltage and a low-pass filter for filtering the a.c. voltage.
An advantageous embodiment of the apparatus implementing the procedure of the invention is also characterized in that the inverter power stage comprises an energy storage device connectable to the d.c. voltage circuit.
An advantageous embodiment of the apparatus implementing the procedure of the invention is also characterized in that the inverter contro
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Lahtinen Matti
Pyorre Ismo
Dynawatt Oy
Wong Peter S.
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