Circuit for regulating the high-voltage supply of an electrostat

Details Circuit for regulating the high-voltage supply of an electrostat Circuit for regulating the high-voltage supply of an electrostat

1987-04-28

1989-03-28

Wong, Peter S.

Electric power conversion systems

Current conversion

Including d.c.-a.c.-d.c. converter

363 41, 363 97, 323903, H02M 3335

Patent

active

048169790

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention is based on a circuit arrangement according to the preamble of the main claim. Electrostatic filters are known which are used in industrial plants for separating dust particles from exhaust gases. These electrostatic filters are connected to high-voltage supplies whose voltage is regulated. The output voltage is fed to a regulator which controls the high voltage. A suitable high voltage can be produced in a simple manner for the electrostatic filters used in industrial plants by means of the available mains voltage. For an application in motor vehicles, where there is only a d.c. voltage of 12 volts, for example, as vehicle voltage, the known circuit arrangements are not suitable for the high-voltage supply of soot filters. The electrostatic filter is operated in the motor vehicle in sharply diverging areas. Throughput, composition, soot charging, moisture and temperature of the exhaust gas vary considerably within the entire speed and load ranges of the motor and change abruptly in intermittent operation of the motor. The impedance of the discharge and the breakdown limit of the discharge depend heavily on these parameters and fluctuate accordingly. The current which is fed into the filter and/or the operating voltage must be correspondingly adjusted to predetermined values in order to ensure a proper functioning of the filter in the entire motor operating range. It must be taken into consideration that the electrostatic filters in motor vehicles must be operated particularly intermittently and with throughput fluctuations of a factor of 10, whereas the known filters in large-scale plants are operated substantially steadily with a fixed operating point.


SUMMARY OF THE INVENTION

The circuit arrangement, according to the invention, with the characteristic features of the main claim, has the advantage that an optimal action of the electrostatic filter can be achieved within the entire motor operating range with this regulator. This effectiveness criterion is satisfactorily met when it is ensured within the entire performance graph of the motor operation that a determined base current I.sub.G is always fed to the electric filter. The regulating circuit can then be designed in a very simple manner as a fixed-value regulator for the filter operating current control variable. The regulation of the high-voltage supply is designed in such a way that it is first always attempted to regulate the base current at a fixed value which is constant and independent of the motor operating point or other disturbing influences to a great extent. Only in a precision optimization of the filter operation can the output current which forms the filter operating current also be controlled, in addition, as a function of the performance graph of the motor operation.
A high voltage which makes it possible to use electrostatic filters in motor vehicles can be generated from a relatively low battery d.c. voltage by means of a diode blocking oscillator. The high-voltage output stage is fed on the primary side with a pulsating voltage whose pulse-duty factor is adjusted as a function of the operating state of the soot filter. A monitoring of the output voltage, output current and output power makes it possible to change the pulse-duty factor in such a way that predetermined maximum values are not exceeded, the power elements employed are protected against destruction by means of a power limiting, and the power absorption is kept as low as possible as a whole.
The diode blocking oscillator can be arranged in multiple stages in a cascade connection in order to increase the output voltage, wherein the charging capacitor can be formed by means of the capacitance of the high-voltage cable on the output side. A special charging capacitor can accordingly be dispensed with.
The primary winding of the blocking oscillator is preferably connected in series with a field effect transistor which is operated as an electric switch, its control input (gate) being controlled by a pulse-width modulator for adjus

REFERENCES:
patent: 4335414 (1982-06-01), Weber
patent: 4410934 (1983-10-01), Fathauer et al.
patent: 4466051 (1984-08-01), Fitzgerald
patent: 4479164 (1984-10-01), Siegel
patent: 4586120 (1986-04-01), Malik et al.

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