Circuit breaker

Abstract

The invention relates to a solid-state circuit breaker (SSCB) for switching or interrupting a power supply, the circuit breaker being formed by at least one switching transistor (3) and an energy absorber (2) in parallel with the at least one switching transistor (3). According to the invention, the SSCB comprises a leakage current measurement circuit (5) which is in series with the energy absorber (2). The SSCB allows the energy absorber to be monitored for functional defects due to aging, thus ensuring safe operation.

Description

[0001] 202420355

[0002] 1

[0003] Description

[0004] Power electronic switch

[0005] The invention relates to a solid state circuit breaker.

[0006] Advances in the development of semiconductor devices have led to new switching concepts that can replace conventional, typically electromechanical switches, particularly in low-voltage applications. These new concepts apply, for example, to circuit breakers or motor starters, but can also be used, in principle, for switching higher currents, such as with power switches. The fast response times of the semiconductor devices are of central importance, as they prevent damage from overload. This means the switch interrupts the current before damage occurs to the installation or the equipment used, or before the semiconductor components of the protective device are destroyed as a self-protection measure.

[0007] In semiconductor-based protective switching devices, also known as solid-state circuit breakers (SSCBs), the switching energy is not converted into an arc as in a mechanical switching device, but rather into heat via an additional circuit called an energy absorber. During disconnection, the disconnection energy comprises the energy stored in the circuit, i.e., in the network, line, or load impedances (consumer impedances). To relieve the energy absorber, the current flowing at the moment of disconnection must be as low as possible. This also applies in the case of a short circuit, where the current rises very rapidly. Rapid short-circuit detection allows for early detection of a short circuit and prevents excessively high short-circuit currents. During a disconnection process, the semiconductor-based protective switching device interrupts the circuit almost instantaneously, within picoseconds.High currents do not occur, and the load on the energy absorber of a semiconductor-based protective switching device is reduced. Known methods for short-circuit detection or disconnection criteria are typically based on determining and evaluating the actual current value.

[0008] Solid-state switches or SSCBs today typically consist of a power electronic switch (LE switch, e.g., IGBT, MOSFET, JFET, etc.) and an energy absorber (e.g., TVS diode, MOV, RC circuits and combinations thereof).

[0009] Especially with MOVs (metal oxide varistors), this can lead to a 202420355 in application.

[0010] 2

[0011] An aging process occurs, altering the electrical properties. The operating voltage, or blocking voltage, at which the varistor can be safely operated continuously often decreases. This drop in operating voltage leads to an increase in leakage current, which, combined with the applied voltage, causes the component to heat up. In the long term, this leads to component failure, and the solid-state switch would no longer be able to reliably interrupt the circuit. In the worst case, the heating process leads to complete thermal destruction of the component, which can endanger nearby equipment and systems, and in the worst case, pose a risk to people.

[0012] The invention aims to increase the safety of SSCBs.

[0013] The problem is solved by an SSCB according to claim 1. Advantageous further developments are specified in the dependent claims.

[0014] The SSCB according to the invention is designed for switching or interrupting a power supply. It comprises at least one switching transistor or power semiconductor (e.g., two antiparallel power semiconductors for a bidirectional SSCB) and an energy absorber arranged in parallel to the at least one switching transistor. Additionally, the SSCB includes a leakage current measuring circuit, which is arranged in series with the energy absorber (and thus also in parallel with the at least one switching transistor).

[0015] The term SSCB, or power electronic switch, refers to any switch designed to interrupt an electrical circuit using a switching transistor or power semiconductor. Examples include circuit breakers, power switches, contactors, and starters. The switch may also include an electromechanical disconnect device, which may be required by standards or be part of the switching concept (e.g., in hybrid switching architectures).

[0016] The switch allows the energy absorber to be monitored for age-related malfunctions, thus ensuring the safe operation of the SSCB.

[0017] According to a further development of the SSCB according to the invention, the leakage current measuring circuit is formed with a bypass path, which includes a voltage-dependent resistor element, and a measuring path, which are arranged in parallel to each other. "Voltage-dependent resistor element" here refers to a component or combination of components which is suitable for changing the 202420355

[0018] 3

[0019] These components are designed with resistance. Typically, this involves a reduction in resistance under critical conditions that are detrimental to the components used (high voltages). The voltage-dependent resistive element is, for example, a metal oxide varistor, a TVS diode, an RC circuit, or a combination thereof.

[0020] According to one embodiment, the SSCB according to the invention is formed with an optocoupler and configured for transmitting leakage current information obtained by means of the leakage current measuring circuit to an evaluation device. The transmission is carried out using the optocoupler, and the primary side of the optocoupler is integrated into the leakage current measuring circuit. The evaluation device (e.g., microprocessor) is galvanically isolated from the main current path by the optocoupler. The primary side of the optocoupler can be arranged in parallel with the measuring path. The optocoupler can additionally be protected against excessively high voltages by means of a protective circuit (e.g., a parallel TVS diode).

[0021] According to one embodiment, the SSCB can include an evaluation unit that checks leakage current information regarding compliance with a criterion and, if necessary, generates a warning message. In a further development of this embodiment, the SSCB includes a measuring sensor for measuring the voltage drop across the at least one switching transistor and is configured to transmit the measured voltage drop to the evaluation unit. The evaluation unit is then configured to use a criterion that depends on this voltage drop.

[0022] According to one embodiment of the SSCB according to the invention, the energy absorber is formed with at least one resistive element, and this at least one resistive element is dimensioned larger than the voltage-dependent resistive element of the leakage current measuring circuit, so that, on the one hand, the voltage supply of the leakage current measuring circuit is ensured, and on the other hand, no excessively high loads occur on elements of the leakage current measuring circuit during normal operation. This at least one resistive element can also be a voltage-dependent resistive element. In one embodiment of the SSCB, the energy absorber is formed with a MOV, and the voltage-dependent resistive element of the leakage current measuring circuit is designed for slower aging compared to the MOV. During dimensioning or design, it is preferably ensured that the voltage drop across the leakage current measurement is sufficient for the functioning of the SSCB.

[0023] 4

[0024] suitable for leakage current measurement in the relevant working area, without causing damage to the components of the leakage current measurement.

[0025] The invention is described in more detail below using an exemplary embodiment. The figures shown are...

[0026] Fig. 1: the structure of an SSCB,

[0027] Fig. 2: the basic structure of the core components of an electronic interrupt unit of an SSCB,

[0028] Fig. 3: a circuit according to the invention and

[0029] Fig. 4: a section of the circuit according to the invention from Fig. 3.

[0030] Fig. 1 shows a representation of a typical SSCB (cf. e.g. DE 102022201960 A1), which can be used to protect a low-voltage electrical circuit. A neutral conductor connection NG (line-side), a phase conductor connection LG (line-side), a neutral conductor connection NL (load-side), and a phase conductor connection LL (load-side) are arranged in a housing GEH. A power source is connected to the GRID side and a load to the LOAD side.

[0031] The main components of the switch are a power supply unit (NT), a control unit (SE), an electronic interruption unit (EU), and a mechanical disconnection unit (MK). The control unit (SE) switches on the electronic interruption unit (EU) and sends an enable signal to the mechanical disconnection unit. The mechanical disconnection unit (MK) includes contacts (KKN and KKL) for opening and closing the phase and neutral conductors.

[0032] For recording current and voltage values, a current sensor unit Sl is provided in the phase conductor path, a first voltage sensor unit SU1 is provided to determine the voltage level between a grid-side connection point EUG and a load-side connection point EUL of the electronic interruption unit EU, and a second voltage sensor unit SU2 is provided to determine the voltage level between the grid-side neutral conductor connection NG and the grid-side phase conductor connection LG. 202420355

[0033] 5

[0034] Fig. 2 shows two components of an electronic interrupt unit, namely a power electronic switching device 1 (referred to in the figure as the ‘LE switch’) and an energy absorber or ‘energy absorber’ 2 (i.e. a circuit or device for converting switching energy into heat).

[0035] Measuring the leakage current through the energy absorber 2 proves rather difficult. The leakage current is usually very small (a few pA-mA), whereas the operating current when the power semiconductor 1 is switched off, especially in the event of a short circuit, is very large (many amps up to the kA range). Furthermore, the leakage current also depends on the actual voltage (Ucb) applied across the switch.

[0036] Fig. 3 shows an SSCB which, according to the invention, has been supplemented by a device 5 for measuring the leakage current ("leakage current measurement"). This device was added to the two functional blocks "LE switch" 1 and "energy absorber" 2 from Fig. 2, which are known from the prior art. Fig. 3 shows further details of an exemplary SSCB known from the prior art. This SSCB is formed with two power semiconductors 3, each of which has a diode connected in parallel (intrinsically or explicitly). The power semiconductors are, for example, IGBTs, MOSFETs, or JFETs, which are driven by a driver 4. The energy absorber 2 is formed, for example, with a TVS diode, a MOV, a varistor, RC circuits, or a combination of these elements.

[0037] The leakage current measurement 5 comprises the following two functional units (see Fig. 4):

[0038] 1) Bypass path 8: In the event of the SSCB's LE switch 1 being switched off, the current commutated to the energy absorber 2 is predominantly carried by this current path (the resistance RMess of the measurement path carries only a very small current). It consists of one of the known components 10 for constructing an energy absorber (e.g., TVS diode, MOV, etc.). The design is such that the voltage drop across this component is significantly smaller (e.g., <20V) than the voltage drop across the "energy absorber," ensuring, with simple means, that the bypass path 8 either does not age significantly (different technology, no MOV) or that aging (e.g., an age-related decrease in the clamping voltage, i.e., the voltage at which a suppressor diode conducts the maximum current) has no impact on the circuit's functionality.The design preferably ensures that the voltage is high enough to drive a current through the optocoupler diode, but low enough not to damage the diode in reverse bias. Therefore, for 110V applications, the ratio of 202420355 is used.

[0039] 6

[0040] Voltage drops across the leakage current measurement 5 and across the energy absorber 2 should be approximately 1:10 ... 1:40, and for 1500V applications 1:50 to 1:300.

[0041] 2) Measurement path 9: When the SSCB is switched off, virtually no current flows through bypass path 8. Therefore, the voltage drop across the leakage current measurement 5 is primarily determined by the resistor Rmess and the series connection of Rv and the primary side of the optocoupler 11. The resistor Rmess sets the trip current through the resistor Rv and the optocoupler (or its primary side 11, e.g., LEDs). Depending on the design, the resistor Rmess and / or the resistor Rv can also be omitted entirely. The leakage current of the energy absorber 2 now flows through the optocoupler 6. On the secondary side of the optocoupler 6, this signal can be evaluated by the microcontroller 7. If the leakage current is too high, the user can be warned, or a controlled shutdown of the system component can be initiated early (via another switching element or a higher-level protection device).The microcontroller 7 can additionally take into account the voltage across the switch (Ucb) if it is measured (which is typically the case with SSCBs - see Fig. 1) and also monitor the aging of the energy absorber 2.

[0042] The optocoupler can also be protected against excessively high voltages by means of a protective circuit (e.g., a parallel TVS diode).

[0043] There are optocouplers on the market that switch to the "on" state at just a few pA of forward input current, such as the HCPL 47XX (ifmin=40pA). This is significantly less than acceptable leakage currents in the MOV, meaning a standard optocoupler can be used.

[0044] This solution enables simple, cost-effective leakage current measurement. This allows for the early detection of uncontrolled failures or malfunctions of the switch.

[0045] The invention can be used in particular for low-voltage switches or low-voltage circuits, but is not limited to this. Low voltage refers to voltages up to 1000 volts AC or up to 1500 volts DC. In particular, low voltage refers to voltages higher than extra-low voltage, defined as 50 volts AC or 120 volts DC. 202420355

[0046] The invention is suitable for a variety of products in which power semiconductors are used to interrupt a circuit, e.g. hybrid contactors, electronic relays, AC and DC protection and power switches, etc.

Claims

202420355 8 Patent claims 1. SSCB for switching or interrupting a power supply, comprising at least one switching transistor (3) and an energy absorber (2) arranged in parallel to the at least one switching transistor (3), characterized in that The SSCB comprises a leakage current measuring circuit (5) which is arranged in series with the energy absorber (2).

2. SSCB according to claim 1, characterized by the fact that the leakage current measuring circuit (5) is formed with a bypass path (8) which includes a voltage-dependent resistance element (10) and a measuring path (9) which are arranged parallel to each other.

3. SSCB according to claim 2, characterized by the fact that The voltage-dependent resistive element (10) is a metal oxide varistor, a TVS diode, an RC circuit or a combination thereof.

4. SSCB according to any one of claims 1 to 3, characterized by the fact that the SSCB is formed with an optocoupler (6) and is designed for transmitting leakage current information obtained by means of the leakage current measuring circuit (5) to an evaluation device (7) using the optocoupler (6), wherein the primary side of the optocoupler (6) is integrated into the leakage current measuring circuit (5).

5. SSCB according to any one of claims 2 to 4, characterized by the fact that the primary side of the optocoupler (6) is arranged parallel to the measurement path (9).

6. SSCB according to claim 5, characterized by the fact that The optocoupler is protected from excessively high voltages by means of a protective circuit.

7. SSCB according to any one of claims 2 to 6, characterized by the fact that 202420355 9 The SSCB includes an evaluation unit which checks leakage current information regarding compliance with a criterion and, if necessary, generates a warning message.

8. SSCB according to claim 7, characterized by the fact that - the SSCB includes a measuring sensor for measuring the voltage drop (lieb) across at least one switching transistor and is designed to transmit the measured voltage drop (lieb) to the evaluation unit, and - the evaluation unit is set up to use a criterion that depends on this voltage drop (lieb).

9. SSCB according to any one of claims 2 to 8, characterized by the fact that - the energy absorber (2) is formed with at least one resistance element, and - this at least one resistance element is dimensioned so much larger than the voltage-dependent resistance element (10) of the leakage current measuring circuit (5) that, on the one hand, the voltage supply of the leakage current measuring circuit (5) is ensured, and on the other hand, no excessively high loads occur on elements of the leakage current measuring circuit (5) during normal operation.

10. SSCB according to any one of the preceding claims 2 to 9, characterized by the fact that the energy absorber (2) is formed with a MOV and the voltage-dependent resistance element (10) is designed for slower aging compared to the MOV.

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