Patent Application
20100289603
This application is a U.S. National Phase application under 35 U.S.C. §371of International Application No. PCT/EP2008/002909, filed Apr. 12, 2008. The International Application was published in German on Jan. 15, 2009 as WO 2009/006952 A1 under PCT Article 21 (2).
The invention relates to a control apparatus for a switching device, in particular for an overvoltage release or an overload circuit breaker, with a pull-in coil and/or holding coil comprising a pulse width-controlled switching mechanism which is connected to the pull-in coil and/or holding coil, and a control unit which is connected to the switching mechanism and generates a control signal with an adjustable pulse width, and also relates to a method for controlling the current flowing through the pull-in coil and/or holding coil.
DE 299 09 901 U1 describes a control apparatus for a contactor drive in which the control apparatus comprises a pulse width-controlled electronic switching mechanism which is connected in series to a drive coil, and a control circuit which is connected on the output side to the switching mechanism. The contactor drive has two active switching states, namely response and holding of the coil. For this purpose, two characteristic value tables with setpoints are stored in the control circuit. In addition, two circuits for the two different switching states are used to determine the momentary drive coil voltage. The two determined measured values for the drive coil voltage are transmitted to the control circuit. For converting the signals, the control circuit has two signal inputs with analog-digital converters connected upstream.
EP 0 789 378 A1 describes a control apparatus for a contactor drive which consists of a series circuit of a drive coil, a switching transistor and a precision resistor for delivering a measured value from the coil current. The measured value is supplied to a control circuit which determines a control signal for the switching transistor based on the measured value, the input voltage of the control apparatus and the switching state of the contactor drive.
Determining a coil current is complex in terms of measurement technology and controlling the current which flows through the coil is time-consuming.
In an embodiment, the present invention provides a control apparatus for a switching device including a contactor drive and a coil. The control apparatus comprises a pulse width-controlled switching mechanism connected to a coil and a control unit connected to the switching mechanism. The control unit is configured to generate a control signal having an adjustable pulse width and set the adjustable pulse width as a function of an input voltage signal so as to maintain a current through the coil approximately constant. The control unit is configured to determine a voltage of the control apparatus by determining an instantaneous coil voltage of the coil from the input voltage signal and based on a pulse width modulation time. The control unit is configured to adjust a current pulse width modulation turn-on time in accordance with the instantaneous coil voltage using at least one data processing unit. The at least one data processing unit is configured to compare the instantaneous coil voltage of the coil with a predetermined coil voltage setpoint stored in the control unit so as to determine the current pulse width modulation turn-on time for the control signal of the control unit.
In the following, the invention will be described in detail with reference to an embodiment illustrated in the drawings, in which:
In one embodiment, a simplified control apparatus is provided for a switching device, in particular for an overvoltage release or an overload circuit breaker, with a pull-in coil and/or holding coil. The control apparatus keeps the current approximately constant through the pull-in coil and/or holding coil of the switching device, without having to store characteristic value tables in a control unit.
In a further embodiment, the control apparatus includes a control unit configured to determin a pulse width of a control signal as a function of an input voltage signal of the control device such that the control apparatus keeps the current approximately constant through the pull-in coil and/or holding coil of the switching device.
In another embodiment, a method is provided for controlling the current flowing through a pull-in coil and/or holding coil of a switching device in that the input voltage of the switching device is established and a pulse width modulation signal for controlling a switching mechanism is determined as a function of a predeterminable voltage setpoint of the coil voltage such that the switching mechanism keeps the current approximately constant through the pull-in coil and/or holding coil of the switching device.
Thus, the control apparatus according to the invention keeps the current approximately constant through the switching device by means of a voltage measurement. A setpoint for the voltage at the coil of the switching device can be predetermined at the control apparatus as a function of the type of switching device. If the switching device as an overvoltage release or overload circuit breaker has a pull-in coil and/or holding coil and if the input voltage of the control apparatus is a direct voltage or an alternating voltage, the current is adjusted by the switching device to an approximately constant value. This is achieved by an approximately constant coil voltage and has proved to be very advantageous due to the reduced circuit expense compared to a measurement of current for adjusting a constant coil current.
The control apparatus controls the voltage at the coil of the switching device such that it corresponds to the predetermined desired voltage of the coil, independently of the switching state, response or holding of the coil.
The control signal with a controllable pulse width for the switching mechanism is generated by a control unit. The control unit is connected on the input side, for example to a voltmeter for detecting the level of the input voltage signal which transmits a current input voltage signal to the control unit. The control unit determines a current control signal with a current pulse width as a function of the transmitted input voltage signal, so that the switching mechanism keeps the coil voltage approximately constant at the coil of the switching device.
The control apparatus advantageously keeps the voltage at the current through the switching device constant independently of the switching state of the switching device (response procedure or holding operation). This avoids a complex measuring step of the current which flows through the switching device.
In order that the control apparatus can keep the current constant which flows through the pull-in coil and/or holding coil of the switching device, the coil voltage which is currently at the switching device is advantageously determined. At least one scanning device is advantageously provided for scanning the input voltage currently present in each case. This scanning device which can be part of the voltmeter scans the prevailing input voltage at predeterminable times or, if appropriate, continuously. The input voltage value determined by the voltmeter is then multiplied with the quotient of the duration of the presence of a voltage signal at the control unit (switch on time) and the period of the pulse width-modulated control signal. The resulting coil voltage value is advantageously compared with a predeterminable coil voltage setpoint and a new turn-on time for the pulse width modulation is determined therefrom.
The pulse width-controlled switching mechanism advantageously comprises a switching transistor. In a further embodiment, the switching transistor is a field effect transistor, in particular an enhancement-type n-channel field effect transistor. An advantage of using such a field effect transistor is that it can be controlled via a voltage, in this case directly via the voltage output by the control unit.
The control signal with adjustable pulse width for the switching mechanism can be generated by a pulse generator. In this case, the control unit transmits to the pulse generator the determined current pulse width of the control signal. The pulse generator can be provided separately from the control unit, thereby reducing the complexity of the control unit.
Alternatively, the pulse generator is advantageously integrated into the control unit, as a result of which the control unit can itself directly generate the control signal with an adjustable pulse width. This measure avoids having to provide a separate pulse generator.
The control unit of the control apparatus advantageously comprises at least one data processing unit for processing data, as a result of which the control unit can rapidly and efficiently detect and process the data for determining the respectively currently prevailing pulse width of the control signal. The data processing unit more preferably comprises a microcontroller. A microcontroller of this type is economical and can easily be adapted to a respective field of application.
A control unit generally has a low-resistance impedance, while a voltmeter has a high-resistance impedance. For this reason, it proves to be advantageous for the control unit to comprise an impedance converter for adapting the impedance of the high-resistance voltmeter to the low-resistance impedance of the control unit. Consequently, a voltmeter which can be used for determining the input voltage signal of the control unit is loaded only minimally and the accuracy of the detectable measured values is increased.
An impedance converter of this type advantageously comprises at least one operational amplifier, as this can be used in an economic and versatile manner. Furthermore, an operational amplifier has the advantage over discrete circuitry that stabilisation of the operating point and compensation of the temperature behaviour are unnecessary.
The data processing unit generally operates internally with digital signals. An analog signal on the input side, in this case an analog measuring signal of the voltmeter for determining the input voltage signal of the control unit should, therefore be converted. For this purpose, the data processing unit comprises an analog-digital converter which converts the analog signals into digital signals to be further processed in the data processing unit.
The switching device comprises a coil, which includes a pull-in coil and/or holding coil for actuating the overvoltage release and/or overload circuit breaker. When an alternating voltage is present on the input side, it is therefore advantageous for the control apparatus to have on the input side a rectifier circuit for rectifying an alternating voltage at the input of the control apparatus.
Furthermore, the input voltage signal of the control apparatus can also comprise, in addition to a direct voltage proportion, alternating voltage portions which can be filtered out by an advantageously provided filter circuit. A filter circuit of this type can be provided on the input side of the control apparatus.
Alternative embodiments of the control apparatus are possible, depending on the field of use of the control apparatus. Thus, for example, it is advantageous if the control method can be implemented continuously, if the input voltage of the control unit is subject to strong fluctuations. However, in other circumstances, it can also be useful if the control method can be implemented at specific adjustable times (electively), for example if it can be foreseen that the input voltage only changes at specific times. To detect such a change, implementation of the method is provided after the change in the input voltage. The accuracy with which the control apparatus keeps the current constant through the switching device can depend on the frequency of the control procedures. In order for the control apparatus to be used as flexibly as possible, it has proved to be advantageous to be able to carry out the control in an intermittent manner, in addition to the continuous and elective control, i.e. the control is carried out regularly at the same time interval, it being possible to adjust the time between two control procedures.
Provided that the accuracy of holding the current by the pull-in coil and/or holding coil of the switching device depends, inter alia, on the frequency at which the control is carried out, it is advantageous if the time between two control procedures is not greater than 150 82 s, and preferably not greater than 70 μs.
The control unit 4 compares the momentary calculated coil voltage USp at the pull-in coil/holding coil 2 with a coil voltage setpoint USp, setpoint stored in the control unit 4 and changes the pulse width of the control signal as a function of the compared value, so that the switching mechanism 3 keeps the coil voltage USp approximately constant at the pull-in/holding coil 2. The control unit 4 requires the momentary input voltage U at the control apparatus 1 for comparison with the coil voltage setpoint USp, setpoint. The input voltage U is made available to the control unit 4 via a voltmeter 5, it being possible for a scanning device 6 to be provided for scanning the input voltage U.
An alternating voltage at the input of the control apparatus 1 is converted into a direct voltage by a rectifier circuit or filter circuit 7, a conversion into a pulsating direct voltage being sufficient. The direct voltage is present at the scanning device 6 and also at the coil 2.
The value, determined by the voltmeter 5, of the input voltage U of the control apparatus 1 is an analog measured value. In order to adapt this analog measured value to the digital further processing in the microcontroller 8, an analog/digital converter A1 is provided at the input of the microcontroller 8. Using the digitalised value of the input voltage of the control apparatus 1, the prevailing time tOn of the pulse width modulation (=pulse width modulation turn-on time) and the period tPWM (=pulse width modulation time), the microcontroller 8 determines the coil voltage USp momentarily present at the pull-in/holding coil 2 which the microcontroller 8 compares with a stored coil voltage setpoint USp, setpoint. The microcontroller 8 generates a new control signal having an adapted pulse width as a function of the comparative value.
In the next step 12, the coil voltage USp is compared with the predeterminable coil voltage setpoint USp,setpoint. This takes place in a controller (see
In the last step 13, the control signal is generated with the new pulse width PWM and is forwarded to the switching mechanism 3, as indicated in
In addition to the embodiments, described above and illustrated in the drawings, one skilled in the art would appreciate that numerous other embodiments are also possible in which a respective adjustable pulse width of a control signal is adjusted as a function of a detectable input voltage of the control apparatus such that the voltage at the pull-in and/or holding coil and thus the current flowing through said pull-in and/or holding coil is kept approximately constant.
While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 031 995.0 | Jul 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP08/02909 | 4/12/2008 | WO | 00 | 6/8/2010 |
