Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-09-16
2001-11-20
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S317000
Reexamination Certificate
active
06320297
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for low loss control of a capacitive load C
P
, particularly a piezoelectric actuator.
With respect to electrical control, piezoelectric actuators behave in the same way as capacitors, which are charged either from a current source or a voltage source. Piezoelectric actuators are normally actuated via a so-called RC control. With this method, the piezoelectric actuator is charged from a voltage source, e.g. a large capacitor, by way of a switch and an ohmic resistance. The switch is opened for the discharging and a second switch is closed, subsequently short-circuiting the piezoelectric actuator via another ohmic resistance. The charging curve and thus also the elongation curve of the piezoelectric actuator can be selected freely owing to the choice of resistances. The great disadvantage of the RC control is the high power consumption of large actuators, meaning for a correspondingly high capacitance and high operating frequencies. In the process, the energy W=CU is converted in the resistances and the actuator into dissipation heat during each charging cycle and discharging cycle.
SUMMARY OF THE INVENTION
It is the object of the invention to develop a method for controlling piezoelectric actuators, which method for the most part reduces the electrical losses. That is, it is an object of the invention to develop a low-loss, and therefore energy-saving, circuit for activating piezoelectric actuators.
This object is solved according to the invention in that at the start of the load control, a capacitor bank is charged from a voltage source to the operating voltage of the capacitive load C
P
, that the load C
P
is charged from the capacitor bank via a series resonant circuit formed by a reactance coil of a freewheeling diode and the load C
P
. If a load is required in this case, the load C
P
is connected via a discharge switch to the reactance coil, which is connected via a freewheeling diode to the capacitor bank, so that the load C
P
can be discharged, except for a residual voltage. The advantage of this method is that when switching the load case, the residual load initially remains on the capacitive load C
P
and that subsequently this residual load can be conducted back to the capacitor bank, so that the residual load for the most part can be reclaimed.
According to one embodiment of the method according to the invention, it makes sense to briefly connect the reactance coil to a ground to reclaim the residual load from the capacitive load C
P
, so that the residual load can be discharged to the capacitor bank. As a result of connecting the reactance coil briefly to ground, it is possible to regain the complete reactive power that was stored in the load.
Based on another embodiment of the method according to the invention, it is advantageous and particularly useful if the capacitor bank is much larger than the capacitive load C
P
. In this way, a maximum voltage transformation ratio, e.g. with factor 2, can be achieved between the source voltage and the load voltage. Above all, this is the case if the capacitor bank capacitance is practically infinite in relation to the capacitance of load C
P
.
Above all, the method according to the invention has the particular advantage that the full load operation voltage from the capacitor bank is available after the capacitor bank is charged to the operating voltage. Adjusting the voltage at the capacitor bank to a stable initial state permits a stable and reproducible charging of the capacitive load C
P
. The voltage at the capacitor bank as well as the voltage at the load C
P
can be used as input variable for the adjustment.
REFERENCES:
patent: 4109174 (1978-08-01), Hodgson
patent: 5204576 (1993-04-01), Mitsuyasu
patent: 5208505 (1993-05-01), Mitsuyasu
patent: 5543679 (1996-08-01), Morino et al.
patent: 5691592 (1997-11-01), Gunderson et al.
patent: 6081061 (2000-06-01), Reineke et al.
patent: 44 35 832 A1 (1996-04-01), None
patent: 0 871 230 A1 (1998-10-01), None
Patent Abstracts of Japan, vol. 016, No. 282 (M-1269), Jun. 23, 1992 (JP 04071859).
Dusterhoft Martin
Flecke Thomas
Gurich Gunter
Dougherty Thomas M.
FEV Motorentechnik GmbH & Co. Kommanitgesellschaft
Kinberg Robert
Venable
Voorhees Catherine M.
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