Electricity: single generator systems – Automatic control of generator or driving means – Plural conditions
Reexamination Certificate
2001-08-07
2004-04-06
Nguyen, Tran (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Plural conditions
C322S026000, C322S028000
Reexamination Certificate
active
06717385
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The present application is based on and claims priority from Japanese Patent Application 2000-238621 filed Aug. 7, 2000, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a voltage regulator of a vehicle AC generator for controlling current supplied to a field coil of the generator by a semiconductor element.
2. Description of the Related Art
Japanese patent publications P2529237 and P3019377, which was filed by this applicant, disclose arts (hereinafter referred to as the turn-off moderation technology) for reducing electromagnetic noises caused by inductance of a power line that connects a semiconductor elements and a battery when the semiconductor element is turned off to cut current supplied to a field coil.
In this turn-off moderation technology, the control voltage or a switching capacity of the semiconductor element is changed at a constant rate so that current-reduction rate of the semiconductor element can be made smaller than the current-reduction rate of the semiconductor element whose control voltage is changed stepwise.
However, the disclosed turn-off moderation technology, a large amount of internal loss may be caused during turnoff transition period of the semiconductor element if the current reduction rate lowers. Since it is necessary to increase the surface area of the semiconductor element and to improve the cooling structure thereof, such turn-off moderation technology has not been put into practice.
In particular, a large amount of heat is generated during the former stage of the turn-off transition period due to a large inductance of the field coil.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above stated problem of the conventional technology.
Therefore, a main object of the invention is to provide a voltage regulator of a vehicle AC generator, in which heat generated by a semiconductor element when current supplied to the field coil is reduced and noises are suppressed.
A voltage regulator of a vehicle AC generator according to a feature of the invention is comprised of a semiconductor element for controlling current supplied to a field coil of the AC generator, a flywheel element connected in parallel with the field coil, a voltage regulating circuit that controls the semiconductor element to turn on or off, and a switching capacity control circuit for controlling a current-switching capacity of the switching element during a former stage of a turn-off transition period of the semiconductor element to be larger than that during the latter stage of the turn-off transition period.
Accordingly, comparing with an ordinary turn-off operation that reduces current switching capacity stepwise during the former stage of the turn-off transition period, the current change rate between the main electrodes can be reduced to be less thereby to increase a period for reducing the turn-on current of the semiconductor element to zero, so that surge voltage and electromagnetic wave, which are proportional to current change rate, can be reduced.
Comparing a conventional turn-off moderation technology that maintains the switching capacity reduction rate (which is the same as the current reduction rate of the semiconductor element) constant from the former stage to the last stage of the turn-off transition period, the necessary turn-off transition period can be shortened. Therefore, not only heat generation can be reduced but also frequency components of electromagnetic noises that are inversely proportional to the turn-off transition period can be changed. As a result, electromagnetic noises that are harmful to electronically controlled on-vehicle devices can be suppressed.
In order to change the current of the semiconductor element from a turn-on current to zero in an ideal step shape, the surge voltage of the battery power line is related to a product of the differentiated value of current change and wire inductance of battery power line. The magnitude of the surge voltage becomes larger as the frequency increases. On the other hand, AC impedance (1/j&ohgr;c) at the space around the battery power line for each frequency component of the surge voltage decreases as the frequency increases. Therefore, the magnitude of the electromagnetic noises radiated outward from the battery power line when the semiconductor element turns off increases in proportion to a square of the frequency. Thus, the magnitude of the electromagnetic noises becomes much larger when the current of the semiconductor element is turned off stepwise. However, since the turn-off transition period is very short, heat generation during the turn-off transition period is very small.
If the current switching capacity, which depends on voltage applied to a control gate of the semiconductor element, is reduced at a fixed reduction rate, the current reduction rate during the turn-off transition period decreases in inverse proportion to increase in the turn-off transition period. Therefore, the electromagnetic noises can be very much reduced. However, the heat generation by the semiconductor element during the turn-off transition period increases that much.
According to this feature, a medium characteristic of both turn-off technologies can be provided, so that the electromagnetic noises can be suppressed without large heat generation.
In other words, the electromagnetic noises generated during the turn-off transition period are suppressed much more than the case of the stepwise change, and mean value of the current during the turn-off transition period and the length of the turn-off transition period can be reduced to less than the turn-off moderation technology.
Moreover, according to this feature, increase in the electromagnetic noises can be effectively suppressed, as described below, although the current switching capacity is reduced during the former stage of the turn-off transition period, and although the current does not decrease very much and the voltage drop across the main electrodes of the semiconductor element is very large, which otherwise causes large heat because of the accumulated magnetic energy of the field coil.
According to another feature of the invention, the drive means changes control voltage or control current of the semiconductor element at an approximately fixed change rate during the former stage of the turn-off transition period and the latter stage, and the change rate at the former stage is set larger than the change rate at the latter stage.
According to this feature, the current switching capacity can be changed by a simple circuit. In the meantime, the control voltage or the control current is the potential or the current of the control gate of the semiconductor element.
According to another feature of the invention, the semiconductor element carries out a follower operation. The follower operation is operation of a circuit in which the field coil and the flywheel diode are connected to the source electrode or the emitter electrode.
In case of the N-channel MOSFET, because the inductance of the field coil in a source follower circuit is very large, when the gate voltage of the semiconductor element decreases during the former stage of the turn-off transition period, magnetic energy of the field coil is discharged to maintain the current supplied to the field coil, thereby lowering the potential of the source electrode.
The reduction of the source voltage suppresses the current change of the semiconductor element, because the channel current of the N-channel MOSFET is proportional to a square of the voltage Vgs between the gate and the source in the saturation range. On the other hand, reduction of the source electrode potential causes increase in voltage effect of the N-channel MOSFET or the semiconductor element and in heat generation.
At the former stage of the turn-off transition period, although the current switching capacity of the semiconductor element decreases due to decrease in the gate electrode potentia
Asada Tadatoshi
Watanabe Kazuyuki
Denso Corporation
Gonzalez Julio C.
Nguyen Tran
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