Solid state circuit breaker

Abstract

The present invention provides a solid-state circuit breaker comprising: a power semiconductor which can be provided in a current loop to conduct or cut off a current; the energy absorber is connected to the power semiconductor in parallel; a sensor for sensing an electrical signal; the control unit is configured to receive the electric signals and control on and off of the power semiconductors based on the electric signals, the energy absorber comprises a plurality of MOV groups which are connected in parallel, each MOV group is connected with a switch in series, and the switch is connected with the power semiconductors in parallel. The control unit is further configured to control the switches to be switched on and switched off so that the MOV sets corresponding to the switched-on switches can absorb energy needing to be released by the current loop when the power semiconductor is switched off, and each MOV set comprises at least one MOV.

Description

Technical Field

[0001] The invention belongs to the field of circuit breakers, and in particular relates to a solid-state circuit breaker. Background Art

[0002] A circuit breaker is a switching device that can close (also called conduction), carry and interrupt (also called interruption) the current under normal circuit conditions and can close, carry and interrupt the current under abnormal circuit conditions within a specified time, such as short circuit, overload or other emergency situations.

[0003] Solid-state circuit breakers (SSCBs) are one of the intelligent forms of circuit breakers, which can replace traditional mechanical circuit breakers for circuit protection. Solid-state circuit breakers are contactless switching devices. Unlike traditional circuit breakers, their on and off are achieved by controlling the carriers and carrier channels inside the semiconductor power device. In the on state, a carrier channel is formed inside the device, the carriers are excited in large quantities, and the device's ability to conduct current is enhanced; in the off state, the carrier channel inside the device disappears, and the device blocks the flow of current. The structural block diagram of the solid-state circuit breaker in the prior art is shown in the figure. Figure 1 As shown, it includes a power semiconductor 100 (such as a triode), an energy absorber 102, a current sensor 104, a controller 106 and a driver 108, wherein the power semiconductor 100 and the energy absorber 102 are connected in parallel in a current loop, and the current sensor 104 is used to sense the current in the current loop. When a fault occurs in the current loop (such as a short circuit, overload, etc.), the current sensor 104 sends an abnormal current signal to the controller 106, and the controller 106 controls the driver 108 to turn off the power semiconductor 100. However, for example, when the current loop is short-circuited or overloaded, turning off the power semiconductor 100 will cause a large amount of inductive energy to accumulate in the current line, and therefore, the energy absorber 102 is usually required to absorb the inductive energy and finally realize the circuit protection function. Summary of the invention

[0004] Therefore, the object of the present invention is to overcome the defects of the prior art and provide a solid-state circuit breaker, comprising:

[0005] Power semiconductors, which can be placed in a current loop to switch the current on or off;

[0006] an energy absorber connected in parallel to the power semiconductor;

[0007] A sensor for sensing an electrical signal;

[0008] a control unit configured to receive the electrical signal and control the on and off of the power semiconductor based on the electrical signal,

[0009] The energy absorber includes a plurality of MOV groups connected in parallel with each other, each of the plurality of MOV groups is connected in series with a switch, and the control unit is further configured to control the on and off of the switch so that the MOV group corresponding to the turned-on switch is sufficient to absorb the energy that needs to be released by the current loop when the power semiconductor is turned off, and each of the plurality of MOV groups includes at least one MOV.

[0010] According to the solid-state circuit breaker of the present invention, preferably, the at least one MOV is connected in series or in parallel.

[0011] According to the solid-state circuit breaker of the present invention, preferably, each of the plurality of MOV groups includes more than two MOVs.

[0012] According to the solid-state circuit breaker of the present invention, preferably, the more than two MOVs are connected in series, in parallel, or in series-parallel.

[0013] According to the solid-state circuit breaker of the present invention, preferably, the switch is a mechanical switch, a circuit breaker or a relay.

[0014] According to the solid-state circuit breaker of the present invention, preferably, the control unit includes a controller and a driver, and the controller is configured to receive the electrical signal and control the driver based on the electrical signal to drive the power semiconductor to be turned on and off.

[0015] According to the solid-state circuit breaker of the present invention, preferably, each of the plurality of MOV groups has the same configuration or a different configuration.

[0016] According to the solid-state circuit breaker of the present invention, preferably, the control unit is configured to control at least a portion of the plurality of switches corresponding to the plurality of MOV groups to be turned on simultaneously.

[0017] According to the solid-state circuit breaker of the present invention, preferably, the control unit is configured to control only one of the plurality of switches corresponding to the plurality of MOV groups to be turned on.

[0018] According to the solid-state circuit breaker of the present invention, preferably, the control unit comprises:

[0019] A data collection module configured to collect operation data;

[0020] a storage module configured to store reference data;

[0021] a timer configured to record a trip time of each of the plurality of MOV groups; and

[0022] A judgment module is configured to judge whether a currently turned-on switch needs to be turned off based on a comparison between the operation data and the reference data or a comparison between the tripping time and the reference data.

[0023] Compared with the prior art, the solid-state circuit breaker of the present invention is easy to operate, low in cost and small in size. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which:

[0025] Figure 1 It is a structural block diagram of a solid-state circuit breaker in the prior art;

[0026] Figure 2 is the voltage-current (VI) characteristic curve of MOV;

[0027] Figure 3 is a structural block diagram of a solid-state circuit breaker according to an embodiment of the present invention;

[0028] Figure 4 A flow chart of a switching strategy of a MOV of a solid-state circuit breaker according to an embodiment of the present invention; and

[0029] Figure 5 4 is a structural block diagram of a controller according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail by specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Currently, the most widely used energy absorber is the metal oxide varistor (MOV), whose voltage-current (VI) characteristic is as follows Figure 2 As shown, the inventors have found that due to the differences in MOV materials and manufacturing processes, the VI characteristic curve of the actual MOV ( Figure 2 The dashed lines in the figure show the actual VI characteristic curves of the two MOVs compared with the ideal VI characteristic curves ( Figure 2 The solid line 1) in the graph will have deviations, for example Figure 2The current deviation 2 at a specific voltage and the voltage deviation 3 and 4 at a specific current in the figure. In practical applications, when the SSCB is turned off, a higher current and energy will be generated, and multiple MOVs are usually required to absorb the energy in series or in parallel. The parallel application of multiple MOVs will not only increase the leakage current, but also cause current inequality due to the VI characteristic deviation between different MOVs, which will cause the performance of the MOV with a larger current to deteriorate due to thermal aging, shortening the service life of the MOV. For an energy absorber containing multiple MOVs, damage to one of the MOVs will cause the entire energy absorber to fail, seriously affecting the service life of the SSCB.

[0032] An embodiment of the present invention provides an improved SSCB, such as Figure 3 The structural block diagram of the SSCB according to an embodiment of the present invention is shown, which includes a power semiconductor 300, an energy absorber 302, a current sensor 304, a controller 306 and a driver 308, wherein the power semiconductor 300 is arranged in a current loop for conducting or disconnecting the current, the current sensor 304 senses the loop current and sends a current indication signal to the controller 306, the controller 306 controls the driver 308 to shut down the power semiconductor 300 when the current is abnormal, and the energy absorber 302 is connected in parallel to the power semiconductor 300 and is used to absorb the energy accumulated in the current loop when the power semiconductor 300 is turned off. In this embodiment, the energy absorber 302 includes N MOV groups B1, B2...B connected in parallel to each other. N Each MOV group includes at least one MOV, preferably at least two MOVs, and a switch (such as relays K1, K2, ... K N ). In an embodiment of the present invention, the controller 306 controls the state of the switch so that at least one switch is in the on state, so that the MOV group corresponding to the on switch is at least sufficient to absorb the energy released by the SSCB when the current loop is turned off once. "Sufficient to absorb" here should be understood as being able to absorb the energy released by the SSCB when the current loop is turned off once, without exceeding the necessary limit. For example, the energy absorption capacity of the MOV group corresponding to the on switch is 100%, 110%, 120%, 150%, or 200% of the energy released by the SSCB when the current loop is turned off once. In particular, only one switch is in the on state, and the rest of the switches are in the off state. For example, relay K1 is turned on first, and relays K2...K N Keep disconnected, that is, use the first MOV group B1 to absorb energy. When the life of the first MOV group B1 ends, disconnect the relay K1, and then turn on the relay K2 to use the second MOV group B2 to absorb energy, and so on, until all MOV groups B1, B2...B N When the service life of the energy absorber 302 ends, a new energy absorber 302 is replaced.

[0033] Those skilled in the art can understand that, in practical applications, the voltage boundary is determined according to the selection of power semiconductors. Since the MOV and the power semiconductor are connected in parallel, according to the principle that the MOV can limit the voltage of the power semiconductor within the boundary during short-circuit energy absorption, the MOV connection mode is preset, including series connection, parallel connection and series-parallel connection. In the embodiment of the present invention, the series-parallel connection mode refers to a series-parallel combination connection. Generally, for high-power SSCBs, parallel MOVs are usually used because the energy to be absorbed during short circuit is very large.

[0034] The inventors have found that in addition to the nonlinear voltage-current characteristics of MOV, nonlinear absorption will also affect its service life. Considering the performance deterioration caused by the current sharing imbalance between multiple MOVs, in order to achieve a certain amount of energy absorption, when using multiple MOVs, a certain margin must be considered. The more MOVs used at the same time, the more serious the imbalance, and the higher the margin requirement, that is, the more MOVs that need to be set up additionally, which will further make the imbalance more serious. For example, if you want to absorb 100J of energy 100 times, considering the margin, 100 MOVs are connected in series and parallel and used together; when they are grouped, for example, divided into 10 groups, each with 10 MOVs, and each group is used alone, then the current imbalance of 10 MOVs is much smaller than that of 100 MOVs, and the performance deterioration caused by the current imbalance is significantly reduced. Therefore, the grouped MOVs can absorb more energy than the ungrouped MOVs. If it is still required to absorb 100J of energy 100 times, 10 groups of MOVs, 9 MOVs in each group, a total of 90 MOVs can be achieved, which significantly saves the number of MOVs. In addition, each MOV group includes at least two MOVs, compared with only one MOV, which can save a large number of switches. Therefore, the SSCB of the embodiment of the present invention has low cost and small size.

[0035] The design steps of an energy absorber according to an embodiment of the present invention are as follows, wherein the energy absorber includes a plurality of MOV groups, and only one MOV group is opened at a time:

[0036] Step 1: Analyze the short-circuit tripping characteristics of the SSCB using operating parameters (e.g., operating voltage, operating current, maximum current protection value, fault breaking time, etc.) and power line infrastructure parameters (e.g., line cable selection, etc.), and calculate the SSCB tripping energy (i.e., the energy that the MOV needs to absorb when a short circuit occurs in the line) and the maximum current.

[0037] Step 2: Preliminarily select the number of MOVs and relays for each MOV group based on the SSCB tripping energy and current. The setting of each MOV group is directly related to the energy that the SSCB needs to absorb each time it trips, and is at least sufficient to absorb the energy released by a trip. Specifically, select the MOV voltage value based on the maximum voltage boundary allowed by the power semiconductor and the rated voltage of the line, and then determine the setting of the MOV group based on the tripping energy and current size and the expected number of MOV parallel branches. The greater the tripping energy and current, the more MOVs the MOV group contains.

[0038] Step 3: Consider the required number of trips within the SSCB life, MOV derating and redundancy requirements, and calculate the number of MOV groups. Specifically, the number of MOV groups required is designed based on the alternative MOV life curve, MOV derating curve and the margin to be reserved.

[0039] Step 4: Using leakage current, MOV current sharing and degradation, fine-tune the number of MOV groups and the number of MOVs in each group by iterating steps 2 and 3. In particular, build a mathematical or simulation model of SSCB short-circuit protection in the system to simulate the characteristics between different groups, and then set some indicators, such as voltage and current stress, life, design margin, short-circuit time, etc., to optimize or fine-tune different designs.

[0040] Step 5: Design the MOV system, including the selection of the switching switch and the switching strategy. Those skilled in the art will appreciate that, in one embodiment of the present invention, the switching switch corresponding to each MOV group may be any switching element known in the art, including a mechanical switch, a circuit breaker, a relay, etc.

[0041] See also Figure 4 The switching strategy of the energy absorber of one embodiment of the present invention is shown, and the switching strategy is executed by the controller 306 .

[0042] First, the SSCB is operated within the rated current and performs protection;

[0043] Then, the operation data is collected, including the number of the MOV group currently in use, the number of trips of the current MOV group, and the current and time characteristics of the most recent protection action. The current characteristics specifically include the current change characteristics during the occurrence of a short circuit and the operation of the SSCB.

[0044] The controller pre-stores different short-circuit absorption curves, the maximum total tripping time of each MOV group, and the number of MOV groups. When the current characteristics are abnormal or the total tripping time exceeds the maximum value, it switches to the next MOV group, and the MOV code is +1 until all MOV groups are exhausted. Specifically:

[0045] Determine whether the current and time characteristics are abnormal.

[0046] If the current and time characteristics are abnormal, further determine whether the MOV group number is equal to the maximum value. If not, switch to the next MOV group and increase the MOV group number by 1. If the MOV group number is equal to the maximum value, report the end of the MOV life to the central controller.

[0047] If the current and time characteristics are normal, further determine whether the total tripping time of the current MOV group is equal to the maximum value allowed. If not, maintain the current state for operation. If equal to the maximum, further determine whether the number of the MOV group is equal to the maximum. If not, switch to the next MOV group and increase the number of the MOV group by 1. If the number of the MOV group is equal to the maximum, report the end of the life of the MOV to the central controller.

[0048] like Figure 5 As shown, the controller 306 according to one embodiment of the present invention includes:

[0049] The data acquisition module 30601 is configured to collect operation data, including the current of the current loop, the number of the MOV group currently in use, the number of trips of the current MOV group, and the current and time characteristics of the most recent protection action.

[0050] The storage module 30602 is configured to store the short-circuit absorption curve, the maximum total tripping time of each MOV group, the number of MOV groups, and the current threshold.

[0051] A timer 30604 is configured to record the tripping time of each MOV group.

[0052] The judgment module 30603 is configured to judge whether the current and time characteristics are abnormal. Specifically, the current and time characteristics of the most recent protection action provided by the data acquisition module 30601 are compared with the short-circuit absorption curve provided by the storage module 30602. When the current and time characteristics deviate from the short-circuit absorption curve, it indicates that the current and time characteristics are abnormal.

[0053] When the current and time characteristics are normal, the judgment module 30603 further determines whether the tripping time of the current MOV group reaches the maximum allowed value. Specifically, the judgment module 30603 is also configured to compare the tripping time provided by the timer 30604 with the maximum total tripping time of each MOV group provided by the storage module 30602.

[0054] When the current and time characteristics are abnormal, or the tripping time of the current MOV group reaches the maximum allowable value, the judgment module 30603 further judges whether the number of the MOV group provided by the data acquisition module 30601 is equal to the number of MOV groups provided by the storage module 30602 (i.e., the maximum value of the MOV group number). If it is not equal to the maximum value, it switches to the next MOV group and increases the number of the MOV group in the data acquisition module 30601 by 1; if the number of the MOV group is equal to the maximum value, an alarm signal S1 is issued, reporting to the central controller that the life of the MOV has ended.

[0055] In addition, when the current data provided by the data acquisition module 30601 is greater than the current threshold value provided by the storage module 30602, the judgment module 30603 sends an indication signal S2 to disconnect the power semiconductor.

[0056] According to other embodiments of the present invention, the controller 306 includes a counting unit integrated in the data acquisition module 30601 or independent of the data acquisition module 30601, which is used to collect and record the number of the MOV group currently in use.

[0057] According to other embodiments of the present invention, power semiconductors are not limited to triodes, but also include rectifier diodes, power transistors (power MOSFET, insulated gate bipolar transistor IGBT), thyristors and other power devices known in the art.

[0058] According to other embodiments of the present invention, the abnormal state of the current loop is sensed by a voltage sensor.

[0059] According to other embodiments of the present invention, each MOV group in the energy absorber has the same configuration or different configurations.

[0060] According to other embodiments of the present invention, MOVs are grouped according to actual conditions, and only one MOV group may be enabled in sequence, or multiple MOV groups may be enabled at one time, which can be achieved by operating the switch through the controller.

[0061] Although the present invention has been described through preferred embodiments, the present invention is not limited to the embodiments described herein but includes various changes and modifications that may be made without departing from the scope of the present invention.

Claims

1. A solid-state circuit breaker, comprising: Power semiconductors, which can be placed in a current loop to switch the current on or off; an energy absorber connected in parallel to the power semiconductor; A sensor for sensing an electrical signal; a control unit configured to receive the electrical signal and control the on and off of the power semiconductor based on the electrical signal, The energy absorber includes a plurality of MOV groups connected in parallel with each other, each of the plurality of MOV groups is connected in series with a switch, and the control unit is further configured to control the on and off of the switch so that the MOV group corresponding to the turned-on switch is sufficient to absorb the energy that needs to be released by the current loop when the power semiconductor is turned off, and each of the plurality of MOV groups includes at least one MOV.

2. The solid-state circuit breaker according to claim 1, wherein: The at least one MOV is connected in series or in parallel.

3. The solid-state circuit breaker according to claim 1, wherein: Each of the plurality of MOV groups includes more than two MOVs.

4. The solid-state circuit breaker according to claim 3, wherein: The more than two MOVs are connected in series, in parallel, or in series and parallel.

5. The solid-state circuit breaker according to any one of claims 1 to 4, wherein: The switch is a mechanical switch, a circuit breaker or a relay.

6. The solid-state circuit breaker according to any one of claims 1 to 4, wherein: The control unit includes a controller and a driver, wherein the controller is configured to receive the electrical signal and control the driver based on the electrical signal to drive the power semiconductor to be turned on and off.

7. The solid-state circuit breaker according to any one of claims 1 to 4, wherein: Each of the plurality of MOV groups has the same configuration or a different configuration.

8. The solid-state circuit breaker according to any one of claims 1 to 4, wherein: The control unit is configured to control at least a portion of the plurality of switches corresponding to the plurality of MOV groups to be turned on simultaneously.

9. The solid-state circuit breaker according to claim 8, wherein: The control unit is configured to control only one of the plurality of switches corresponding to the plurality of MOV groups to be turned on.

10. The solid-state circuit breaker according to claim 9, wherein: The control unit comprises: A data collection module configured to collect operation data; a storage module configured to store reference data; a timer configured to record a trip time of each of the plurality of MOV groups; and A judgment module is configured to judge whether a currently turned-on switch needs to be turned off based on a comparison between the operation data and the reference data or a comparison between the tripping time and the reference data.

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