Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2001-01-26
2002-03-26
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S132000, C363S017000
Reexamination Certificate
active
06362985
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a power transmission device and a method of transmitting power, especially to a power transmission device and a method of transmitting power to a commercial electricity system.
BACKGROUND ART
When a direct current (DC) electric power is supplied to a commercial electricity system, the DC voltage is inverted to an alternating current (AC) voltage by an inverter, and then the inverted voltage is supplied to a commercial electricity system. The DC electric power is generated by a generator such as a solar battery and the like. The inverter modulates the voltage waveform by the pulse width modulation (PWM) to correct the error (difference) between the inverted AC waveform and the voltage waveform of a commercial electricity system.
For the PWM, a complex control circuit is required to control the frequency and phase of the voltage. This control circuit raises the price of the power transmission device as well as complicates the structure of the power transmission device.
And in the case where the inverter is damaged, there is a possibility of electric power generated by the generator leaking to a commercial electricity system without being controlled. Further, there is a possibility of devices connected to a commercial electricity system being damaged by an electricity leakage (i.e., a possibility of a secondary damage being caused).
DISCLOSURE OF INVENTION
The present invention was made in view of the above circumstances, and it is the first object of this invention to provide a power transmission device and a method of transmitting power which are simply composed.
Further, it is the second object of this invention to provide a power transmission device and a method of transmitting power which are low-cost.
And it is the third object of this invention to provide a power transmission device and a method of transmitting power which can prevent electricity from leaking from a generator to a commercial electricity system and consequently can prevent the occurrence of the secondary damage.
To achieve the above objects, the power transmitting device according to the first aspect of this invention is located between an AC (alternating current) power source (
8
) for generating an AC voltage and a DC (direct current) power source (
2
,
3
,
4
, and
5
) for generating a DC voltage, and comprises:
a transfer switch (
6
) which is connected to between the DC power source and the AC power source and is for supplying the DC voltage to the AC power source or interrupting a supply of the DC voltage to the AC power source in accordance with a control signal provided thereto; and
an AC voltage monitor circuit (
7
) which is connected to the AC power source and the transfer switch and is for determining whether an absolute value of the AC voltage generated by the AC power source is equal to or higher than a predetermined threshold level or not, supplying the transfer switch with the control signal for controlling the transfer switch to supply the DC voltage to the AC power source in such a way as to provide the DC voltage with the same polarity as the AC voltage when determining that the absolute value is equal to or higher than the threshold level, and supplying the transfer switch with the control signal for controlling the transfer switch to interrupt the supply of the DC voltage to the AC power source when determining that the absolute value is lower than the threshold level.
According to this structure, the DC voltage output by the DC power source is supplied to the AC power source via the transfer switch or interrupted to be supplied depending on whether or not the AC voltage generated by the AC power source is higher than the voltage threshold level. Accordingly, there is no need for pulse-width modulation (PWM) and a complex control circuit necessary for PWM. Therefore, the structure will be simple.
An output impedance of the DC power source may be higher than that of the AC power source, and a voltage drop generated in an outside load which is connected to the AC power source by an electric current supplied from the DC power source may be higher than the AC voltage generated by the AC power source.
In this case, the voltage between both ends of the load is maintained approximately equal to the AC voltage generated by the AC power source.
The AC voltage monitor circuit may further comprise a half cycle monitor circuit (
104
) for determining whether or not a period of time in which the DC power source is supplying the DC voltage to the AC power source is over a half of a cycle of an AC electric power generated by the AC power source, and supplying the transfer switch with the control signal for controlling the transfer switch to interrupt the supply of the DC voltage from the DC power source to the AC power source when determining that the period of time is over the half of the cycle.
According to this half cycle monitor circuit, the AC power source is cut away from the DC power source when the AC power source is out of order so that a period of time in which the DC power source is supplying the DC voltage becomes over the half of the cycle of the AC voltage. Therefore, an electricity leakage from the DC power source to the AC power source can be prevented.
The transfer switch may comprise, for example:
a first switching element (T
1
) which comprises a first electric current path and a first control terminal;
a second switching element (T
2
) which comprises a second electric current path and a second control terminal;
a third switching element (T
3
) which comprises a third electric current path and a third control terminal; and
a fourth switching element (T
4
) which comprises a fourth electric current path and a fourth control terminal. In this case:
one end of the first electric current path and one end of the third electric current path may be connected to one of a pair of electrodes which are provided on the DC power source and are for outputting the DC voltage;
one end of the second electric current path and one end of the fourth electric current path may be connected to the other of the pair of electrodes provided on the DC power source;
the other end of the first electric current path and the other end of the fourth electric current path may be connected to one of a pair of electrodes which are provided on the AC power source and are for outputting the AC voltage; and
the other end of the second electric current path and the other end of the third electric current path may be connected to the other of the pair of electrodes provided on the AC power source.
And in this case, the AC voltage monitor circuit may:
determine whether a polarity of a voltage output from the one of the pair of electrodes provided on the DC power source is same as or different from that of a voltage output from the one of the pair of electrodes provided on the AC power source;
apply a voltage, for controlling the first and second electric current paths to turn on, to the first and second control terminals as the control signal, and apply a voltage, for controlling the third and fourth electric current paths to turn off (non-conductive), to the third and fourth control terminals as the control signal when determining that the absolute value of the AC voltage is equal to or higher than the threshold level, and that the polarity of the voltage output from the one of the pair of electrodes provided on the DC power source is same as that of the voltage output from the one of the pair of electrodes provided on the AC power source;
apply a voltage, for controlling the first and second electric current paths to turn off, to the first and second control terminals as the control signal, and apply a voltage for controlling the third and fourth electric current paths to turn on, to the third and fourth control terminals as the control signal when determining that the absolute value of the AC voltage is equal to or higher than the threshold level, and that the polarity of the voltage output from the one of the pair of electrodes provided on the DC power source is diff
Haneda Masaji
Inoue Someji
Baker & McKenzie
NTT Data Corporation
Vu Bao Q.
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