The present disclosure relates to DC supply systems. Various embodiments may include switching devices for disconnecting a current path in a DC supply system, wherein the current path comprised source-end and load-end inductances.
A switching device for disconnecting a current path in a DC supply system, said current path comprising source-end and load-end inductances, must be capable of accommodating the recovery or removal of energy from the DC supply system. If mechanical switches or hybrid switches with a mechanical and electronic switching element are employed, there is a resulting risk of the generation of an arc, as it cannot be ensured that the disconnection of the current path will coincide with a zero-crossing of the current. A mechanical switching element of this type must therefore be protected by a complex circuit, e.g. by the provision of a plurality of semiconductor switching elements and varistors as voltage surge limiters.
To this end, in some cases, the high-speed mechanical switch arranged in the main current branch can be interconnected with a semiconductor switching element which, in the conducting state, undergoes a low voltage drop. The function of this semiconductor switching element, upon the disconnection of the load path, is to generate a voltage drop upon disconnection, such that the current can be routed to a main switch which is connected in parallel with this arrangement. This main switch is comprised of a series circuit of a plurality of semiconductor switching elements, for the voltage surge protection of which a varistor is parallel-connected in each case. If the current now flows essentially via the parallel path, the high-speed mechanical switch can be disconnected without generating an arc. A disadvantage of this switching device is the complexity thereof, associated with the plurality of semiconductor switching elements and varistors required, wherein the latter are extremely expensive and cumbersome.
Switching devices may be exclusively comprised of controllable semiconductor switching elements, e.g. IGBTs. In variants of this type, for example, two semiconductor switching elements can be connected in the load path in an anti-series arrangement for bidirectional operation. In the absence of further measures, however, this switching device can only be employed in DC supply systems which do not feature any large inductances. Moreover, voltage-limiting components such as e.g. varistors and the like are required, the use of which, however, is not favored, on the grounds of cost.
PCT/EP2018/054775 describes a switching device addressing the problems mentioned above. The switching device comprises at least two series-connected switching modules. Each of the switching modules comprises at least one controllable semiconductor switching element in the form of an IGBT (Insulated Gate Bipolar Transistor), to which a series circuit consisting of a resistor and a capacitor is connected in parallel. A switching device of this type permits a “soft” switch-off process, wherein the current flow in the current path is not reduced abruptly, but with a ramped characteristic. By means of at least one of the at least two switching modules, a counter-voltage is constituted in the current path. This is made possible by operation of the respective semiconductor switching element of the switching modules in the switched-mode domain.
Accordingly, the high power loss in the event of a switch-off is not implemented in the semiconductor switching element of the respective switching modules, but primarily in the resistor of the respective switching modules. Voltage-limiting components, such as varistors, which are expensive, heavy and cumbersome, can thus be omitted from the switching device. The semiconductor switching element in the respective switching modules thus assumes the function of a brake chopper.
A disadvantage of this switching device, however, is that not only the load current, but also the discharge current of the capacitor, is conducted via the controllable semiconductor switching element. Although the discharge current is conducted only briefly during the switch-off operation, IGBTs are capable of carrying an overcurrent only to a slight extent. Therefore, they must be designed for the worst case, that is to say the maximum possible sum current comprising the load current and the discharge current, which makes it necessary to use components of large dimensions. As a result, the switching device may become undesirably expensive.
The teachings of the present disclosure may include switching devices for disconnecting a current path in a DC supply system, said current path comprising source-end and load-end inductances, which switching device is structurally and/or functionally improved further and does not require any overdimensioning of components. In particular, the switching device is intended to be able to be provided at lower cost.
For example, some embodiments include a switching device (1) for disconnecting a current path (6) in a DC supply system, said current path (6) comprising source-end and load-end inductances (3, 5), said switching device comprising at least two series-connected switching modules (10), wherein each of the switching modules (10) comprises at least one controllable semiconductor switching element (13), to which a series circuit consisting of a resistor (14) and a capacitor (15) is connected in parallel, characterized in that the resistor (14) is formed from a series circuit of two series-connected resistors (141, 142), wherein a first end of the series circuit is connected to a first load terminal of the controllable semiconductor switching element (13) and a second end of the series circuit is connected to the capacitor (15), and each of the switching modules (10) also comprises a further controllable semiconductor switching element (16) which is connected between a first node (143) of the two resistors in series circuit and a second node (144) which connects the capacitor (15) to a second load terminal of the controllable semiconductor switching element (13).
In some embodiments, the further controllable semiconductor switching element (16) can be switched to a conducting state and a blocking state via a control signal.
In some embodiments, the further controllable semiconductor switching element (16) is an insulated-gate bipolar transistor (IGBT).
In some embodiments, the further controllable semiconductor switching element (16) is a thyristor.
In some embodiments, the thyristor is of the disconnectable type (GTO, IGCT).
In some embodiments, the thyristor can be turned off by means of a turn-off circuit.
In some embodiments, the controllable semiconductor switching element (13) is an element of the turn-off circuit.
In some embodiments, the turn-off circuit comprises a further capacitor (17) which is connected between the first node and the first load terminal of the controllable semiconductor switching element (13).
In some embodiments, a desired discharge time of the capacitor (15) is set by means of the ratio of the resistance values of the resistors (141, 142) in the series circuit.
The teachings herein are explained in greater detail hereinafter, with reference to exemplary embodiments represented in the drawings, in which:
In the following descriptions, identical elements are provided with the same reference symbols throughout the various figures.
Some embodiments of the teachings herein include a switching device for disconnecting a current path in a DC supply system, said current path comprising source-end and load-end inductances, which switching device comprises at least two series-connected switching modules. Each of the switching modules comprises at least one controllable semiconductor switching element, to which a series circuit consisting of a resistor and a capacitor is connected in parallel.
The teachings herein further develop the switching device known from PCT/EP2018/054775 by virtue of the resistor being formed from a series circuit comprising two series-connected resistors. A first end of the series circuit is connected to a first load terminal of the controllable semiconductor switching element. A second end of the series circuit is connected to the capacitor. Each of the switching modules also comprises a further controllable semiconductor switching element. The further controllable semiconductor switching element is connected between a first node of the two resistors in the series circuit and a second node which connects the capacitor to a second load terminal of the controllable semiconductor switching element.
In the switching devices described herein, the load current flows via the controllable semiconductor switching element, as in the known switching device. In contrast, the discharge current for discharging the capacitor of the switching module is accepted by the further controllable semiconductor switching element. As a result, the controllable semiconductor switching element, which conducts the load current, can be dimensioned for the level of the load current. There is no need for any overdimensioning, as in known switching devices. The switching device provided thereby has lower costs despite the additional components.
In some embodiments, use is made, as a further controllable semiconductor switching element, of a controllable semiconductor switching element which can be switched to a conducting and blocking state via a control signal. For example, the further controllable semiconductor switching element may be an insulated gate bipolar transistor (IGBT). If the further controllable semiconductor switching element is in the form of an IGBT, this results in more degrees of freedom during control. In addition to the function of carrying the discharge current of the capacitor of the switching module, it is also possible to achieve a permanent current flow via the further controllable semiconductor switching element. The resistor in the series circuit of resistors, which is connected upstream of the further controllable semiconductor switching element, can then be used, for example, to attenuate network oscillations or as a load resistor for capacitive loads.
In some embodiments, the further controllable semiconductor switching element is a thyristor. The use of a thyristor as a further controllable semiconductor switching element has the advantage that it can be briefly highly overloaded, with the result that a relatively small type can be used. As a result, the switching device can be implemented at low cost.
In some embodiments, the thyristor is of the disconnectable type, for example a GTO (Gate Turn-Off) thyristor or an IGCT (Integrated Gate-Commutated Thyristor). The use of a thyristor of the disconnectable type makes it possible to end the current flow through the current path of the further controllable semiconductor switching element in a targeted manner.
If it is not intended to use a thyristor of the disconnectable type, in particular on account of high costs and/or poor availability, the thyristor can alternatively be turned off by means of a turn-off circuit. In this case, in particular, the controllable semiconductor switching element which carries the load current of the switching device is an element of the turn-off circuit. As a result, the number of additional elements can be kept low.
In some embodiments, the turn-off circuit comprises a further capacitor which is connected between the first node and the first load terminal of the controllable semiconductor switching element. A further capacitor, which generates a brief negative voltage surge across the thyristor when the controllable semiconductor switching element is switched on, is therefore connected in parallel with that resistor in the series circuit of resistors which is connected in series with the further controllable semiconductor switching element, with the result that the current in the thyristor becomes zero. This makes it possible to turn off the thyristor with little effort.
In some embodiments, a desired discharge time of the capacitor is set by means of the ratio of the resistance values of the resistors in the series circuit. When charging the capacitor, the resistance value which results from the sum of the resistance values of the two resistors in series circuit of resistors is effective. In contrast, when discharging the capacitor, only the resistance value of that resistor which is included in the parallel branch to the further controllable semiconductor switching element is effective.
In some embodiments, the further capacitor has a capacitance value which is less than the capacitance value of the capacitor of the switching module.
The switching device described herein may be used in a DC supply system having a voltage of greater than 1000 V. Depending upon the prevailing voltage in the DC supply system, an appropriate corresponding number of switching modules for the switching device must then be selected. The higher the voltage to be controlled in the DC supply system, the greater the number of switching modules selected will be—subject to the provision of identical semiconductor switching elements. For DC supply systems in the medium-voltage range, IGBTs or MOSFETs can specifically be employed as controllable semiconductor switching elements for switching the load current. At even higher voltages, thyristors having a cut-off device or IGCTs are specifically employed. In some embodiments, it is provided that the switching device of the type described here is employed as a short-circuit-proof power switch.
The basic mode of operation of such an individual switching module of the switching device 1 is as follows: if the switching device 1 is to conduct current, the controllable semiconductor switching element 13 is switched to a conducting state. Immediately after the current path 6 is to be disconnected by means of the switching device 1, the controllable semiconductor switching element 13 is switched to a blocking state by means of a control device which is not shown in the figures. As a result, the current I flowing in the current path 6 can only continue to flow via the RC element constituted by the resistor 14 and the capacitor 15. The capacitor 15 is charged by the current I flowing into it, until a predefined upper threshold value for the voltage dropped across it is achieved. To this end, a corresponding measuring device (not represented) can be provided in the switching module 10. Immediately after the predefined upper threshold value is achieved, the controllable semiconductor switching element 13 is switched back to a conducting state. The capacitor 15 can thus be discharged via the resistor 14 and the controllable semiconductor switching element 13. Immediately after a predefined lower threshold value for the voltage dropped across the capacitor 15 is achieved, the controllable semiconductor switching element 13 is switched back to a conducting state by means of its control device. The controllable semiconductor switching element 13 therefore need not only be designed for the (load) current I to be conducted, but also for the discharge current resulting from the discharge of the capacitor 13.
If the disconnection of the current path 6 occurs in response to a short circuit in the DC supply system, reclosing (switching of the controllable semiconductor switching element 13 to a conducting state) permits the restoration of the flow of short-circuit current through the switching module 10. However, as the switch-on time of the controllable semiconductor switching element 13 is very short, the current I flowing in the current path 6 is cleared on average as the source-end and load-end inductances 3 and 5 (cf.
Were the switching device 1 to comprise only a single switching module 10, as represented in
In order to permit the disconnection of a current path in a DC supply system having higher voltages by means of the switching device 1 proposed, according to
The mode of operation of the switching device shown in
Unlike in the case of the use of a single switching module, in the case of a plurality of switching modules, a counter-voltage (i.e. a voltage which is oriented in opposition to the voltage direction of the DC voltage source 2) is consistently present in the DC supply system. If the number n of series-connected switching modules is very large, the short-term short-circuiting of one switching module is scarcely of any significance, as a result of which the current is cleared gradually.
Immediately after the predefined upper switching threshold in all the controllable semiconductor switching elements 13-i is no longer achieved, all the controllable semiconductor switching elements 13-i of the switching modules 10-i will remain permanently blocked. The voltage in the DC supply system will then oscillate with a natural resonance.
The methods described, independently of the magnitude of the number n of series-connected switching modules, are executed in a corresponding manner. Which of the controllable semiconductor switching elements 13-i, at any given time point, are in a blocking state, and which other controllable semiconductor switching elements 13-i are switched to a conducting state, can be effected by means of deliberate control of the above-mentioned, but unrepresented control unit. Likewise, by means of the appropriate and differing selection of respective upper switching thresholds, the temporal characteristic of the switch-on and switch-off of the associated controllable semiconductor switching element can be influenced.
In some embodiments, the voltage present across the respective capacitors 15-i can be monitored by corresponding measuring means (not shown). The controllable semiconductor switching element assigned to the capacitor on which the highest voltage is present is switched, in this case, to a conducting state, until the predefined lower threshold value is achieved. Given that, consistently, at different time points, different switching modules or the capacitors thereof have the highest voltage, the switch-on and switch-off of the controllable semiconductor switching elements 13-i of the switching modules 10-i occurs in a more or less randomized manner.
In a modification of the switching device 1 known from
The IGBT 16 and the controllable switching element 13 can be switched at approximately the same time. The capacitor 15 is then discharged via the resistor 141 and the IGBT 16. In contrast, when the semiconductor switching elements 13, 16 are switched to a blocking state, the capacitor is charged via both resistors 141, 142. The discharge time of the capacitor 15 can be set by selecting the resistance value 141.
According to the solution shown in
In the implementation variant illustrated in
A known disadvantage of thyristors is that a direct current is not extinguished by itself, with the result that the load current I would continue to flow even after the capacitor 15 has been discharged and when the controllable semiconductor switching element 13 is in a blocked state. In order to solve this problem, a thyristor of the disconnectable type, for example a GTO or an IGCT, can be used as the thyristor 13. However, they have the disadvantage of high costs and poor availability. Alternatively, a so-called turn-off circuit can also be arranged above the thyristor 16. The variant shown in
The two variants described can be used in the arrangements according to
A switch for bidirectional operation can be achieved by connecting two modules in anti-series, as shown and described in
Number | Date | Country | Kind |
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10 2018 215 827.4 | Sep 2018 | DE | national |
This application is a U.S. National Stage Application of International Application No. PCT/EP2019/074758 filed Sep. 17, 2019, which designates the United States of America, and claims priority to DE Application No. 10 2018 215 827.4 filed Sep. 18, 2018, the contents of which are hereby incorporated by reference in their entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2019/074758 | 9/17/2019 | WO | 00 |