Device and method for current-limited switching on of a multi-pole circuit breaker

Abstract

The invention relates to a multi-pole circuit breaker (MCB) with an interrupting device (U1, U2) for each pole. According to the invention, a pre-charge resistor (R1, R2) is connected in parallel to each interrupting device (U1, U2), and the pre-charge resistors (R1, R2) can be switched on or off independently of each other by means of a switch (S1, S2). This flexibility in switching on and off pre-charge resistors allows for an acceleration of the pre-charging process.

Description

[0001] The invention relates to a multi-pole circuit breaker and a method for current-limited switching on of a multi-pole circuit breaker.

[0002] Circuit breakers are used to connect, disconnect, or, in the event of a fault (e.g., short circuit or overcurrent), automatically disconnect subnetworks very quickly. In the case of a DC network, the networks typically have a capacitive characteristic due to storage capacitors. When two subnetworks with different voltage levels are connected, this leads to transient equalizing currents (inrush currents) that are limited only by the ohmic resistance and the line inductance. Typically, these equalizing currents are so high that they must be limited to prevent damage to components.

[0003] A standard procedure for limiting the currents is the use of a pre-charge resistor (also called a "balancing resistor").

[0004] There is a need to improve conventional pre-charging methods and, in particular, to accelerate the pre-charging process. An improved pre-charging method is described in WO 2020 / 058 162 A1. Further improvements are possible. The invention aims to contribute to this.

[0005] International Patent Application WO 2020 / 156689 A1 discloses a method for precharging a second network section with electrical energy from a first network section of a DC network. The method relates to an embodiment in which, in an initial state, the initial voltage prevailing in the second network section is lower than the DC voltage prevailing in the first network section. At a first point in time, the two network sections are connected via a resistive current path that includes a precharging resistor. At a subsequent second point in time, as soon as the voltage in the second network section lies between the initial voltage and the DC voltage, the two network sections are connected via a semiconductor switch arranged in parallel.

[0006] German patent application DE 10 2020 129 919 A1 describes a power converter for transferring power between an AC side and a DC side of the converter, wherein the AC side of the converter can be connected to a grounded three-phase AC supply network and the DC side of the converter can be connected to an ungrounded DC network. The converter has a bridge circuit whose AC terminals can be connected to the AC side of the converter via AC switches and whose DC terminals can be connected to the DC side of the converter via disconnect switches. A DC intermediate circuit of the converter can be charged from the AC supply network via a galvanically isolated AC pre-charge circuit. The converter has an insulation monitor designed to measure the insulation resistance of the DC side of the converter when the AC pre-charge circuit is connected to the DC intermediate circuit.The application further describes a method for supplying an ungrounded DC network from a grounded three-phase AC supply network using a transformerless power converter.

[0007] German patent DE 11 2011 100 448 B4 discloses a circuit for connecting and disconnecting a switchable electrical system and an electrical network of a vehicle, wherein the circuit comprises at least one mechanical main disconnect switch for disconnecting and connecting the switchable electrical system to the electrical network of the vehicle, and at least one pre-charging unit connected in parallel to the main disconnect switch, comprising at least one controllable semiconductor switch, wherein the pre-charging unit comprises at least one mechanical disconnect switch for disconnecting and connecting the switchable electrical system and the electrical network of the vehicle, wherein the semiconductor switch is connected in series with the mechanical disconnect switch, characterized in thatthat at least one pre-charging unit and at least one main disconnect switch are arranged in each of the positive and negative output voltage paths of the switchable electrical system.

[0008] The problem is solved by a multi-pole circuit breaker according to claim 1 and a method for current-limited switching on of a multi-pole circuit breaker according to claim 10. Advantageous embodiments are specified in the dependent claims.

[0009] A multi-pole circuit breaker with a break device for each pole, designed for improved pre-charging, is proposed. This circuit breaker can, in particular, be a circuit breaker capable of switching direct current unidirectionally or bidirectionally. The break devices are preferably formed with semiconductor switches (e.g., MOSFETs or IGBTs).

[0010] The term "circuit breaker" is to be understood as a device intended for operational switching, e.g., for connecting subnetworks. Typically, circuit breakers also have a protective function (short circuit, overload, etc.). However, the term "circuit breaker" as used in the application is not to be interpreted restrictively as requiring a protective function.

[0011] According to the invention, a pre-charge resistor is connected in parallel to each interrupting device, and the pre-charge resistors can be switched on or off independently of each other using a switch (e.g. semiconductor switch).

[0012] This flexibility in switching pre-charge resistors on and off allows for faster pre-charging. It is advantageous for the pre-charge resistors to have different values. Switching the pre-charge resistors on and off is controlled by a dedicated control device (e.g., MCU or CPU). This control device is configured to switch the pre-charge resistors on or off according to a specified total resistance value. For example, in a two-pole circuit breaker with resistors R1 and R2, the total resistance can be essentially the same as the resistance(s) through which the current flows, i.e., R1+R2, R2, or R1. With different resistances, the total resistance can then be reduced in three stages (R1+R2, R2, and R1).Therefore, further training envisages that the control device be set up to switch the pre-charge resistors on or off in order to gradually reduce the overall value for the resistance.

[0013] The point at which the current reduction occurs can be selected so that the current load does not exceed a limit. For this purpose, the multipole circuit breaker can be designed to measure at least one parameter from which a voltage difference between subnetworks connected by the circuit breaker (MCB) or a current flowing through the circuit breaker can be determined during pre-charging (the "at least one parameter" is given, for example, by the voltages on both sides or the current value), to transmit this at least one parameter to the control device, to determine the voltage difference or current, to compare the voltage difference or current with a limit value that has been set to ensure a load-safe transition to the next stage (e.g., so that the current at the next stage does not exceed the current-carrying capacity of the semiconductors), and to adjust the inflow or outflow.Switching off to the next stage occurs when the calculated voltage difference or current falls below the limit value. In the case of a voltage difference, the at least one parameter can comprise the voltages of both sides, the difference (absolute value) of which is then taken, or it can be the current value itself. In this case, determining the current from the parameter is trivial. However, it could also be, for example, a time period, from which the current value is then determined using known relationships. This determination is then preferably carried out by the control device.

[0014] This procedure (determining / measuring parameters and comparing them to limit values) is preferably performed continuously, so that switching on or off to the next stage can be carried out as soon as the load at the next stage is no longer critical. The limit value is typically set with regard to the protection of the circuit breaker components (especially semiconductor components).

[0015] According to a further development of the procedure involving a stepwise reduction of the overall resistance value, an operating procedure is to be carried out for at least one interrupting device to reduce the current value until a criterion for load-independent normal operation is met. This criterion could, for example, consist of equalizing the voltages of subnetworks connected by the circuit breaker (e.g., magnitude(U(subnetwork 1)-U(subnetwork 2))< ε). However, it is also conceivable, for example, that the operating procedure consists of pulsed operation and the criterion concerns falling below a threshold value for the energy transmitted in this operating mode.

[0016] The invention also relates to a method for current-limited switching on of a multi-pole circuit breaker according to the invention.

[0017] The invention is explained in more detail below using an exemplary embodiment and the accompanying figures. These show: Fig. 1: a conventional low-voltage circuit arrangement, Fig. 2: a section of the low-voltage circuit arrangement according to claim 1, Fig. 3: a schematic representation of a conventional circuit breaker, Fig. 4: Current and voltage waveforms when connecting two subnetworks with different voltage levels, Fig. 5: a schematic representation of a circuit breaker according to the invention, Fig. 6a-6e: the circuit breaker of Fig. 5 at different phases of a switching-on process according to the invention, and Fig. 7: a flowchart of a method according to the invention for current-limited switching.

[0018] In Fig. Figure 1 shows a low-voltage circuit arrangement consisting of a digital DC switch 1 with a pre-charge circuit 2, including a mains environment. The digital DC switch 1 has a power semiconductor 3, which is, for example, a MOSFET. The power semiconductor 3 is electrically connected via a capacitor 4 to a varistor 5 and, within a pre-charge circuit 2 connected in parallel, via a resistor 6 to at least one transistor 7 with a diode 8 connected in parallel to it. Additionally, after the transistor 7 with diode 8, another combination of a transistor 9 and a diode 10 is connected in series with the first combination. Fig. Figure 1 also shows a voltage sensing device 11, a control unit 12 for the pre-charging function 2, a control unit 13 for the digital DC switch 1, a current sensing device 14, and a signal processing unit 15, which evaluates the signals from the voltage and current sensing devices 11 and 14 and provides control signals for the control units or drivers 12 and 13. A schematic measurement curve 23 for the voltage across the digital DC switch 1 is also shown.

[0019] Fig. Figure 2 shows a section of the circuit from Fig. 1. The pre-charge resistor 6 can be switched on or off using the transistors 7 and 9.

[0020] The circuit from Fig. 1 and Fig. 2 can be used bidirectionally due to the duplication of the power semiconductors 3 and the transistors 7 and 9. However, the invention is also suitable for unidirectional switching solutions.

[0021] Typically, the circuit consists of Fig. 1 and Fig. 2. Part of a circuit breaker (MCB) through which the DC+ and DC- lines are routed. In Fig. 1 and Fig. Figure 2 shows only elements for interrupting the DC+ line. However, the following assumes that the DC- line can also be interrupted. Fig. Figure 3 schematically shows a circuit breaker LS through which DC+ and DC- lines pass, which can be interrupted by interrupting devices U1 and U2. The interrupting devices U1 and U2 are power semiconductor switching devices equipped with power semiconductors such as MOSFETs – see description in [reference to be added]. Fig. 1 - are formed. With regard to the DC+ and DC- lines, one also speaks of poles or a two-pole circuit breaker. The interrupting devices can be configured as in Fig. 1 and Fig. 2. Designed and controlled.

[0022] Traditionally, it is - as in Fig. 1 and Fig. 2 - only one pole is equipped with a switchable pre-charge resistor R (resistance 6 in Fig. 1 and Fig. 2 for the pole marked DC+). To limit the inrush current, a pre-charge resistor R is typically connected in parallel to this pole of the circuit breaker. This resistor can be activated for pre-charging by means of a semiconductor switch S. With a purely capacitive load C, this results in a charging curve in the form of a first-order lag element (PT1 element) with a time constant τ = R·C. The voltage then follows a curve of the form U(t) = Umax*(1-exp(-t / τ)), as shown in Fig. Figure 4 shows that the voltage would have equalized by 63% after one time constant, and by 86.5% after twice the time.

[0023] Example: Maximum voltage difference ΔUmax = Umax - U(0) = 1000V - 0V = 1000V Maximum pre-charging current or equalization current Imax = 20A, meaning it operates with a resistance value of R = Umax / Imax = 50 ohms. Maximum capacitance: C = 20 mF T = τ = R·C = 50 Ω · 20 mF = 1 s; 2T = 2 s

[0024] This means a pre-charging time of approximately 2 seconds until the voltage has risen to 86% of 1000V.

[0025] In Fig. Figure 4 shows the corresponding waveforms of current and voltage. The equalizing current decreases steadily from Imax (strictly monotonically decreasing curve).

[0026] The resistance value R is chosen such that the maximum current Imax does not endanger the electronics of the circuit breaker LS, i.e., Imax is not higher than the maximum permissible current. The invention is based on the consideration that the drop in the equalizing current during the pre-charging process would allow a reduction in the pre-charging resistance without exceeding the Imax threshold, provided the timing and extent of this reduction are correctly chosen. The invention takes advantage of this fact, implementing it in a particularly cost-effective manner.

[0027] According to the invention, only separately switchable resistors are provided for additional poles, thereby making the pre-charging process controllable. In the specific embodiment, switchable balancing resistors R1 and R2 are provided for both poles, which are switched by dedicated switches S1 and S2. A corresponding power switch LS is shown schematically in Fig. Figure 5 shows that the values ​​of the two resistors add up to the value required for current limiting (in the example above, R1 + R2 = R = Umax / Imax = 50 ohms). It is particularly advantageous if the resistance values ​​of R1 and R2 differ, e.g., R2 = 2 · R1 or R1 = 50 ohms * 1 / 3, R2 = 50 ohms * 2 / 3, and R1 + R2 = 50 ohms.

[0028] One method to speed up the pre-loading process is in Fig. Figures 6a-6e are shown. Initially, the two interrupt devices U1 and U2, as well as the switches S1 and S2, are not conductive ( Fig. 6a). Then, the two pre-charge resistors R1 and R2 are switched on using switches S1 and S2 ( Fig. 6b). In the next step ( Fig. 6c) The semiconductor switch U1 is closed. The current on the DC+ line now flows through this semiconductor switch, meaning the pre-charge resistor now only has the value of R2 = 2 / 3 · R. In the next step, the semiconductor switch U1 is opened again and the semiconductor switch U2 is closed instead ( Fig. 6d). The pre-charge resistance is then reduced to the value of R1 = 1 / 3 · R. Finally, in the last step ( Fig. 6e) The semiconductor switch U1 is closed again, i.e., the pre-charge resistance is zero. Pulsed or clocked operation can then follow, or the power semiconductors in the main current path can be operated in a current-limiting manner. These two options reduce the loads on the power semiconductors and are described in more detail in WO 2020 / 058 162 A1.

[0029] The procedure is in Fig. Figure 7 is shown again as a flowchart. In step S11, the circuit breaker is open and no pre-charging has yet taken place. All switches U1, U2, S1, and S2 are open. No current is flowing. When the circuit breaker is switched on, switches S1 and S2 are closed first for pre-charging; the current-limiting resistor is R1+R1 (step S12). If a threshold condition is met, switch U1 is closed. The threshold can, in principle, relate to the current, voltage, or time (provided that the relationships of Fig. 4 apply).

[0030] In Fig. Step 7 starts with a voltage measurement and sets a voltage threshold SW1 to ensure that the current load is not too high for the following step (query S13). After closing switch U1 (step S14), the resistance has the value R2 (here and generally in this embodiment, it is assumed that the on-resistances of switches U1, U2, S1, and S2 are negligibly small compared to the values ​​of resistors R1 and R2). In step S15, it is checked whether a further voltage threshold SW2 (SW2 < SW1) is undershot, and if so, switch U1 is opened and switch U2 is closed. The resistance then has the value R1 (R1 < R2). Finally, if a third voltage threshold SW3 (SW3 < SW2) is undershot (query S17), switch U1 is closed, and current limiting is implemented by the operating mode until the voltage levels of the subnetworks have equalized.

[0031] The criterion for switching to the next stage is that the voltage difference ΔU between subnetworks connected by the circuit breaker (LS) is (in magnitude) less than a threshold value. If the voltage difference is less than the adjustable threshold for switching to the next stage, the switch to the next stage occurs. For example, a supply bus is connected to a load side. The corresponding voltages on both sides are referred to below as Ubus and Uload. Then the criterion is abs(Ubus-Uload) = ΔU < SW, where "abs" denotes the absolute value and "SW" a threshold value. The set value or adjustable threshold value SW is calculated as: Voltage difference = Imax(20A) * Reffective, where Reffective is the effective resistance of the stage to which switching occurs when the threshold value is undershot, i.e., R2, R1, or the resistance implemented by the operating procedure.

[0032] Referring to Fig. That means 7: S13: abs(Ubus-Uload) < (Imax*R2) = SW1 S15: abs(Ubus-Uload) < (Imax*R1) = SW2 S17: abs(Ubus-Uload) < SW3 (This is the transition to switching on the main current path. The current pulse accepted via the main current path then depends on the load circuit.)

[0033] However, it would also be possible to use a current threshold or current measurement instead of a voltage threshold or voltage measurement: Assuming a total pre-charge resistance of R = Umax / Imax and R = R1 + R2 = 1 / 3·R + 2 / 3·R, and taking Imax as the load capacity threshold, then with a continuously decreasing current profile as in Fig. 4 SW1 ≤ Imax R2 / R = 2 / 3 Imax and SW2 ≤ I-max R1 / R = 1 / 3 Imax.

[0034] The SW3 threshold would then depend on how efficiently the operating procedure can limit the current.

[0035] The advantages of the invention lie not only in a shortened pre-charging time. It also mitigates the problem that continuous loads in the load circuit prevent pre-charging by preventing the voltage from approaching the supply voltage.

[0036] With the resistance ratio of 2:1 mentioned above in the exemplary embodiment, the tolerable load consumption during pre-charging is increased by a factor of 3 compared to conventional methods.

[0037] Furthermore, by cleverly choosing the resistance ratio and the timing of the switching states, an advantageous distribution of the power loss between the two resistors can be achieved.

[0038] The invention was described above in the context of an exemplary embodiment. This embodiment is merely illustrative. Further embodiments are immediately apparent to those skilled in the art. In particular, the invention can also be used with more than two poles for all switch types that operate with a precharge.

Claims

[1] Multipole circuit breaker (MCB), with an interrupting device (U1, U2) for each pole, wherein - each interrupting device (U1, U2) has a pre-charge resistor (R1, R2) connected in parallel, and - the pre-charge resistors (R1, R2) can be switched on or off independently of each other using a switch (S1, S2), - the multi-pole circuit breaker (MCB) is formed with a control device (15) designed for switching the pre-charge resistors (R1, R2) on or off, characterized by , that - the control device (15) is designed to switch the pre-charge resistors (R1, R2) on or off according to a total value for the resistance. [2] Multipole circuit breaker (MCB) according to claim 1, characterized by that the interrupt devices (U1, U2) are formed with semiconductor switches. [3] Multipole circuit breaker (MCB) according to claim 1 or 2, characterized bythat the switches (S1, S2) are semiconductor switches. [4] Multipole circuit breaker (MCB) according to any one of claims 1 to 3, characterized by that the pre-charge resistors (R1, R2) differ in value. [5] Multipole circuit breaker (MCB) according to claim 1, characterized by , that the control device (15) is designed to switch the pre-charge resistors (R1, R2) on or off in order to gradually reduce the total value for the resistance. [6] Multipole circuit breaker (MCB) according to claim 5, characterized by that the multipole circuit breaker (MCB) is designed - for measuring at least one parameter from which a voltage difference between subnetworks connected by the circuit breaker (MCB) or a current flowing through the circuit breaker can be determined during pre-charging, - for the transmission of at least one parameter to the control device (15), - for determining the voltage difference or the current, - for comparing the voltage difference or current with a limit value that was set in the sense of a load-free transition to the next stage, and - for switching on or off in the sense of the next stage, if the calculated voltage difference or the calculated current falls below the limit value. [7] Multipole circuit breaker (MCB) according to claim 5 or 6, characterized by , that the control device (15) is designed to carry out an operating procedure of at least one interrupting device (U1, U2) to reduce the load after the stepwise reduction of the total value for the resistance, until a criterion for load-free normal operation is met. [8] Multipole circuit breaker (MCB) according to any one of claims 1 to 7, characterized by that the number of poles is two. [9] Multipole circuit breaker (MCB) according to any one of claims 1 to 8, characterized by that the circuit breaker (MCB) is designed for switching direct current voltage. [10] Method for current-limited switching on of a multipole circuit breaker (MCB) according to any one of claims 5 to 9, characterized by a gradual reduction of the total value for the resistance by switching pre-charge resistors (R1, R2) on or off. [11] Method according to claim 10, characterized by - Measurement of at least one parameter from which a voltage difference between subnetworks connected by the circuit breaker (MCB) or a current flowing through the circuit breaker can be determined during pre-charging, - Transmitting at least one parameter to the control device (15), - Determination of the voltage difference or current, - Comparison of the voltage difference or current with a limit value that was set to ensure a load-free transition to the next stage, and - Switching on or off in the sense of the next stage if the calculated voltage difference or the calculated current falls below the limit value. [12] Method according to one of claims 10 or 11, characterized by , that after the stepwise reduction of the total value for the resistance, an operating procedure of at least one interrupting device (U1, U2) is carried out to reduce the load until a criterion for load-free normal operation is met.

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