Buffer circuit and method suitable for hybrid direct current circuit breaker and related equipment

Abstract

The invention discloses a buffer circuit and method suitable for a hybrid direct-current circuit breaker and related equipment, and belongs to the technical field of hybrid direct-current circuit breakers. By arranging the buffer diode, the discharge current of the buffer capacitor is prevented from reversely flowing through the UFD, and the turn-off delay of the UFD is avoided; the buffer diode is connected with the charging branch in parallel, so that the charging voltage of the buffer capacitor is slowly increased, the turn-off loss is reduced, and the turn-off reliability of the hybrid direct-current circuit breaker is improved; the parallel connection of the buffer diode and the charge transfer branch can quickly transfer the energy stored in the buffer capacitor to the high-capacity capacitor after current conversion, thereby avoiding the obstruction of the buffer capacitor to the quick starting action of the UFD, reducing the energy loss in the charge transfer process through the introduction of the small-resistance resistor, and improving the efficiency of the UFD. Rapidity and high efficiency of charge transfer are ensured; the buffer diode is connected in parallel with the discharge branch and is used for controlling the discharge speed of the buffer capacitor so as to maintain stable operation of the circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of hybrid DC circuit breakers, and in particular to a buffer circuit of a hybrid DC circuit breaker. Background Art

[0002] In recent years, with the evolution of flexible DC transmission technology from multi-terminal systems to DC power grids, more stringent requirements have been put forward for the reliability, operational stability and safety of the power grid. According to the redundant design principle of the power grid, the power grid must have the ability to isolate faulty lines, that is, when a single line fails, it can quickly cut off and isolate the faulty line to avoid major accidents that cause the entire network to shut down. Therefore, short-circuit fault protection technology has become a key problem that needs to be overcome in the field of flexible DC power grids.

[0003] In practical applications, the combination of DC reactors and hybrid DC circuit breakers is considered an effective solution for short-circuit protection of flexible DC grids. However, with the increase of grid voltage levels, the cost of hybrid DC circuit breakers has increased dramatically, and the design difficulty has also increased accordingly. At the same time, the performance of existing reactors can no longer meet the needs of high-voltage DC grids. Therefore, reducing the cost and design requirements of hybrid DC circuit breakers and exploring new short-circuit fault current limiting technologies have become core issues that need to be urgently addressed in the field of short-circuit fault protection of high-voltage flexible DC grids.

[0004] In the design of hybrid DC circuit breakers, the normal branch is an indispensable and important component, which consists of a mechanical switch (UFD) and a load transfer switch (IGBT-TLCS). Among them, the IGBT-TLCS is the weak link of the hybrid high-voltage DC circuit breaker, and failures often occur during the commutation of the LCS branch. Although the traditional RCD snubber circuit can improve the reliability of the LCS to a certain extent, it will hinder the rapid opening of the UFD, thereby affecting the overall performance of the hybrid DC circuit breaker. Specifically, when the UFD needs to be opened quickly, the capacitor in the RCD snubber circuit may still be in a charging or discharging state. If the capacitor is charging at this time, it will absorb current from the power supply, which may cause the UFD to open more slowly because part of the current is used to charge the capacitor instead of driving the UFD to open; if the capacitor is discharging, it may release the stored charge through the resistor, which will also consume part of the current, thus affecting the rapid opening of the UFD.

[0005] Therefore, how to design a new type of buffer circuit that can not only improve the reliability of the load transfer switch during the LCS branch commutation period but also not affect the rapid start-up of the UFD has become a technical problem that needs to be urgently overcome by current technicians in this field. Summary of the invention

[0006] The object of the present invention is to provide a snubber circuit, method and related equipment suitable for a hybrid DC circuit breaker, aiming to solve the problem of hindering the rapid opening action of the UFD when a traditional RCD snubber circuit is used to improve the reliability of the hybrid DC circuit breaker.

[0007] The present invention solves the above technical problems through the following technical solutions: A snubber circuit suitable for a hybrid DC circuit breaker, comprising a snubber diode D s , buffer capacitor C s , large capacity capacitor C p , small resistance resistor R sp And the large resistance R p ; Snubber diode D s The first branch is connected in parallel with the first branch, the second branch and the third branch respectively. The first branch is the charging branch, which consists of a buffer capacitor C s The second branch is the charge transfer branch, which consists of a large-capacity capacitor C p Connect a small resistance R in series sp The third branch is the discharge branch, which consists of a large resistance resistor R p constitute; When applied, the snubber circuit is connected in parallel to the load transfer switch IGBT-TLCS of the hybrid DC circuit breaker.

[0008] A method for optimizing parameters of a snubber circuit applicable to a hybrid DC circuit breaker adopts the snubber circuit applicable to the hybrid DC circuit breaker and comprises the following steps: S1. Topological structure when constructing buffer circuit application; S2. Based on the topology, draw the LCS branch current i of the hybrid DC circuit breaker LCS and buffer capacitor C s The voltage u cs The relationship curve of the load transfer switch IGBT-TLCS is constructed based on the relationship curve. According to the shutdown model, the equivalent circuit of the buffer circuit at different stages of the shutdown process is obtained. The shutdown process includes three stages: charging process, charge transfer process and capacitor discharge process. S3. Analyze the working principle of the buffer circuit at different stages of the shutdown process and construct the buffer capacitor C s The voltage expression of and the turn-off energy loss expression of the load transfer switch IGBT-TLCS; Based on the voltage expression, plot the buffer capacitor C with different capacitance values s Calculate the snubber capacitor C according to the voltage and current waveforms and switch trajectory of the load transfer switch IGBT-TLCS s The reference value C s1 ; Based on the voltage expression and the turn-off energy loss expression, plot the turn-off energy loss versus the snubber capacitance C s The relationship curve, combined with the reference value C s1 , get the buffer capacitor C s The optimal value range of .

[0009] The present invention is further improved in that: it also includes S4, according to the shutdown model, analyzing and obtaining the collector current of the load transfer switch IGBT-TLCS The expression is:

[0010] Among them, i LS is the fault current; i p is the current of stray inductance; According to the collector current The expression of stray inductance L of different hybrid DC circuit breakers is p The turn-off time t of the load transfer switch IGBT-TLCS f The collector current i during the turn-off process is plotted under the ratio of c 、The voltage u between the collector and emitter of IGBT-TLCS ce and stray inductor current i p Waveform graph; Analyze the waveform and get different L p / t f The influence of the ratio on the turn-off loss, peak voltage and turn-off response time is used to determine L p / t f Based on the optimal ratio, the stray inductance current i is obtained. p With the collector current i c The slope matches the relationship.

[0011] A further improvement of the present invention is that the buffer capacitor C s The voltage expression is as follows: The buffer capacitor C s The charging process [t0, t1],

[0012] Among them, α is the damping coefficient; is the resonant frequency; is the damping frequency; is the turn-off time of the load transfer switch IGBT-TLCS, is the peak current of the current source equivalent to the snubber circuit in the turn-off model, is the buffer capacitor C sThe charging process starts at t1, and t2 is the buffer capacitor C s The end time of the charging process; The buffer capacitor C s The charge transfer process [t1, t2],

[0013] in, The buffer capacitor C at time t1 s The stored charge, τ1 is the charge transfer time constant; t2 is the buffer capacitance C s The end time of the charge transfer process; The buffer capacitor C s The capacitor discharge process [t2, t3],

[0014] Where τ2 is the discharge constant, is the buffer capacitor C s The peak voltage of the buffer capacitor C s The capacitor discharge process ends time.

[0015] A further improvement of the present invention is that the charge transfer time constant τ1 is specifically: .

[0017] A further improvement of the present invention is that the discharge constant τ2 is specifically: .

[0019] A further improvement of the present invention is that the turn-off energy loss expression of the load transfer switch IGBT-TLCS is specifically:

[0020] in, is the turn-off energy loss of the load transfer switch IGBT-TLCS; It is the voltage between the collector and the emitter when the load transfer switch IGBT-TLCS is turned off; is the collector current; I LST At time t1, the current through the current limiting reactor L s The current; is the damping frequency; is the energy loss value; is the collector current angle of the load transfer switch IGBT-TLCS during the turn-off process; is the turn-off time of the load transfer switch IGBT-TLCS; is the buffer capacitor C s The charging process starts at t1, and t2 is the buffer capacitor Cs The charging process ends at the time.

[0021] A further improvement of the present invention is that the buffer capacitor C s The reference value C s1 Specifically:

[0022] in, is the maximum value of the output voltage of the load transfer switch IGBT-TLCS; is the turn-off time of the load transfer switch IGBT-TLCS; At time t1, the current through the current limiting reactor L s The current; The optimal value range of the buffer capacitor Cs is: .

[0024] A chip comprises the buffer circuit as described above.

[0025] An electronic device includes a device body and a chip as described above disposed in the device body. Compared with the prior art, the positive and progressive effects of the present invention are: The buffer circuit for hybrid DC circuit breaker provided by the present invention improves the shutdown reliability of the load transfer switch and ensures stable and rapid shutdown during commutation. By setting a buffer diode, the discharge current of the buffer capacitor is prevented from flowing through the UFD in reverse, thereby avoiding the shutdown delay of the UFD; the parallel connection of the buffer diode and the charging branch causes the charging voltage of the buffer capacitor to increase slowly, reducing the shutdown loss, thereby improving the shutdown reliability of the hybrid DC circuit breaker; the parallel connection of the buffer diode and the charge transfer branch can quickly transfer the energy stored in the buffer capacitor to the large-capacity capacitor after commutation, thereby avoiding the buffer capacitor from hindering the rapid opening action of the UFD, and at the same time, the introduction of a small resistance resistor reduces the energy loss in the charge transfer process, thereby ensuring the rapidity and efficiency of the charge transfer; the buffer diode is connected in parallel to the discharge branch to control the discharge speed of the buffer capacitor, thereby maintaining the stable operation of the circuit.

[0026] Furthermore, the buffer circuit parameter optimization method for a hybrid DC circuit breaker provided by the present invention obtains the optimal value range of the buffer capacitor by constructing a shutdown model, drawing a relationship curve and analyzing the working principle. This can not only improve the performance of the hybrid DC circuit breaker, but also ensure that the circuit breaker can maintain a stable fault protection capability under different working conditions.

[0027] Furthermore, by analyzing different L p / t f i during the shutdown process under the ratio c 、uce and i p Waveform diagram, obtained L p / t f The optimal ratio of is helpful to further optimize the design of hybrid DC circuit breaker and improve its stability and reliability during the shutdown process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings in the specification are used to provide further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0029] Figure 1 It is a diagram of a turn-off model including a snubber circuit; Figure 2 1 is a relationship curve of the LCS branch current iLCS of the hybrid DC circuit breaker and the voltage ucs of the snubber capacitor Cs changing with time, wherein (a) is the relationship curve of the current iLCS, and (b) is the relationship curve of the voltage ucs; Figure 3 It is the turn-off model of the load transfer switch IGBT-TLCS and the equivalent circuits of the buffer circuit at different stages of the turn-off process, wherein Figure (a) is the turn-off model of the load transfer switch IGBT-TLCS, Figure (b) is the equivalent circuit of the charging process, Figure (c) is the equivalent circuit of the charge transfer process, and Figure (d) is the equivalent circuit of the capacitor discharge process; Figure 4 Figure 1 is a voltage and current waveform diagram and a switch trajectory diagram of a load transfer switch IGBT-TLCS corresponding to a buffer capacitor Cs with different capacitance values, wherein Figure (a) is a voltage and current waveform diagram of a load transfer switch IGBT-TLCS corresponding to a buffer capacitor Cs with different capacitance values, and Figure (b) is a switch trajectory diagram; Figure 5 It is the relationship curve between the turn-off energy loss and the snubber capacitance Cs; Figure 6 2 are the shutdown waveforms under different Lp / tf ratios, wherein (a) is the shutdown waveform with a larger Lp / tf ratio, (b) is the shutdown waveform with a smaller Lp / tf ratio, and (c) is the shutdown waveform with a moderate Lp / tf ratio; Figure 7 It is a voltage waveform diagram of the active RCD snubber circuit and the snubber circuit during the commutation process of the LCS branch. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments, which are intended to explain the present invention rather than to limit it.

[0031] See also Figure 1The present invention provides a buffer circuit suitable for a hybrid DC circuit breaker, comprising a buffer diode D s , buffer capacitor C s , large capacity capacitor C p , small resistance resistor R sp And the large resistance R p ; Snubber diode D s The first branch is connected in parallel with the first branch, the second branch and the third branch respectively. The first branch is the charging branch, which consists of a buffer capacitor C s The second branch is the charge transfer branch, which consists of a large-capacity capacitor C p Connect a small resistance R in series sp The third branch is the discharge branch, which consists of a large resistance resistor R p constitute; When applied, the snubber circuit is connected in parallel to the load transfer switch IGBT-TLCS of the hybrid DC circuit breaker.

[0032] By setting a buffer diode, the discharge current of the buffer capacitor is prevented from flowing back through the UFD, thereby avoiding the shutdown delay of the UFD; the parallel connection of the buffer diode and the charging branch causes the charging voltage of the buffer capacitor to increase slowly, reducing the shutdown loss, thereby improving the shutdown reliability of the hybrid DC circuit breaker; the parallel connection of the buffer diode and the charge transfer branch can quickly transfer the energy stored in the buffer capacitor to the large-capacity capacitor after commutation, thereby avoiding the buffer capacitor from hindering the rapid opening action of the UFD. At the same time, the introduction of a small-resistance resistor reduces the energy loss in the charge transfer process, thereby ensuring the rapidity and efficiency of the charge transfer; the buffer diode is connected in parallel with the discharge branch to control the discharge speed of the buffer capacitor, thereby maintaining the stable operation of the circuit.

[0033] The present invention also provides a method for optimizing parameters of a snubber circuit applicable to a hybrid DC circuit breaker, using the snubber circuit applicable to the hybrid DC circuit breaker, comprising the following steps: S1. Topological structure when constructing buffer circuit application; S2. Based on the topology, draw the LCS branch current i of the hybrid DC circuit breaker LCS and buffer capacitor C s The voltage u cs A relationship curve that changes with time; based on the relationship curve, a turn-off model of the load transfer switch IGBT-TLCS is constructed, and according to the turn-off model, an equivalent circuit of the buffer circuit at different stages of the turn-off process is obtained, wherein the turn-off process includes three stages: charging process, charge transfer process and capacitor discharge process; S3. Analyze the working principle of the buffer circuit at different stages of the shutdown process and construct the buffer capacitor C sThe voltage expression of and the turn-off energy loss expression of the load transfer switch IGBT-TLCS; Based on the voltage expression, plot the buffer capacitor C with different capacitance values s Calculate the snubber capacitor C according to the voltage and current waveforms and switch trajectory of the load transfer switch IGBT-TLCS s The reference value C s1 ; Based on the voltage expression and the turn-off energy loss expression, plot the turn-off energy loss versus the snubber capacitance C s The relationship curve, combined with the reference value C s1 , get the buffer capacitor C s The optimal value range of .

[0034] By constructing a shutdown model, drawing relationship curves and analyzing the working principle, the optimal value range of the buffer capacitor is obtained, which can not only improve the performance of the hybrid DC circuit breaker, but also ensure that the circuit breaker can maintain stable fault protection capabilities under different working conditions.

[0035] Specifically, it also includes S4, according to the shutdown model, analyzing the collector current of the load transfer switch IGBT-TLCS The expression is:

[0036] Among them, i LS is the fault current; i p is the current of stray inductance; According to the collector current The expression of stray inductance L of different hybrid DC circuit breakers is p The turn-off time t of the load transfer switch IGBT-TLCS f The collector current i during the turn-off process is plotted under the ratio of c 、The voltage u between the collector and emitter of IGBT-TLCS ce and stray inductor current i p Waveform graph; Analyze the waveform diagram to obtain different L p / t f The influence of the ratio on the turn-off loss, peak voltage and turn-off response time is used to determine L p / t f Based on the optimal ratio, the stray inductance current i is obtained. p With the collector current i c The slope matches the relationship.

[0037] By analyzing different L p / t f i during the shutdown process under the ratioc 、u ce and i p Waveform diagram, obtained L p / t f The optimal ratio of is helpful to further optimize the design of hybrid DC circuit breaker and improve its stability and reliability during the shutdown process.

[0038] Specifically, the buffer capacitor C s The voltage expression is as follows: The buffer capacitor C s The charging process [t0, t1],

[0039] Among them, α is the damping coefficient; is the resonant frequency; is the damping frequency; is the turn-off time of the load transfer switch IGBT-TLCS, is the peak current of the current source equivalent to the snubber circuit in the turn-off model, is the buffer capacitor C s The charging process starts at t1, and t2 is the buffer capacitor C s The end time of the charging process; The buffer capacitor C s The charge transfer process [t1, t2],

[0040] in, The buffer capacitor C at time t1 s The stored charge, τ1 is the charge transfer time constant; t2 is the buffer capacitance C s The end time of the charge transfer process; The buffer capacitor C s The capacitor discharge process [t2, t3],

[0041] Where τ2 is the discharge constant, is the buffer capacitor C s The peak voltage of the buffer capacitor C s The end time of the capacitor discharge process; Specifically, the charge transfer time constant τ1 is: .

[0042] Specifically, the discharge constant τ2 is: .

[0043] Specifically, the turn-off energy loss expression of the load transfer switch IGBT-TLCS is:

[0044] in, is the turn-off energy loss of the load transfer switch IGBT-TLCS; It is the voltage between the collector and the emitter when the load transfer switch IGBT-TLCS is turned off; is the collector current; I LST At time t1, the current through the current limiting reactor L s The current; is the damping frequency; is the energy loss value; is the collector current angle of the load transfer switch IGBT-TLCS during the turn-off process; is the turn-off time of the load transfer switch IGBT-TLCS; is the buffer capacitor C s The charging process starts at t1, and t2 is the buffer capacitor C s The charging process ends at the time.

[0045] Specifically, the buffer capacitor C s The reference value C s1 Specifically:

[0046] in, is the maximum value of the output voltage of the load transfer switch IGBT-TLCS; is the turn-off time of the load transfer switch IGBT-TLCS; At time t1, the current through the current limiting reactor L s of current.

[0047] The optimal value range of the buffer capacitor Cs is: .

[0048] In a specific embodiment of the present invention, a method for optimizing snubber circuit parameters applicable to a hybrid DC circuit breaker is provided, which is specifically implemented according to the following steps: Step 1: construct a novel unidirectional variable time constant RCD (UVRCD) snubber circuit topology, including: Step 1.1, the novel unidirectional variable time constant RCD snubber circuit includes a snubber diode D s , buffer capacitor C s , large capacitance C p , small resistor R sp , large resistor R p ; Step 1.2, build the topology of the UVRCD buffer circuit, see Figure 1 , snubber diode D s Connected in parallel with three branches, the three parallel branches are: ① The buffer capacitor C s ② The charging branch is composed of a large-capacity capacitor C p A small resistor R is connected in series sp The charge transfer branch is composed of a large resistor R p The discharge branch is composed of the buffer diode D s Can effectively prevent C s The discharge current flows through the UFD in the reverse direction, avoiding the UFD shutdown delay and achieving the purpose of reducing the fault current peak. During the IGBT-TLCS shutdown period, the buffer capacitor C s The slow increase of charging voltage effectively reduces the rising rate of IGBT-TLCS turn-off voltage and greatly reduces turn-off loss.

[0049] Step 2: Draw out the main waveform diagram of the new unidirectional variable time constant RCD snubber circuit topology established in step 1, and analyze its working principle according to the equivalent circuits of each stage in the IGBT-TLCS shutdown process, including: Step 2.1, based on the novel unidirectional variable time constant RCD (UVRCD) snubber circuit established in step 1, plot the LCS branch current i LCS and buffer capacitor voltage u cs The relationship curve over time; Step 2.1.1, after the fault current is completely transferred from the LCS branch to the main circuit breaker branch, the current i LCS is equal to zero, the current i p Equal to the current limiting reactor L s The current i flowing through LS . Because I LCS =0, the UFD can be turned off. Therefore, after the fault current is completely commutated from the LCS branch to the main circuit breaker branch, since the UFD has been turned off and there is a snubber diode D s , so that the UVRCD buffer circuit is isolated from the original circuit and becomes an isolated circuit. In this isolated circuit, because R sp About 10Ω, which is very small, resulting in a time constant τ1 (=R sp C s +R sp C p ) is also very small, so the s The charge in will pass through R sp quickly transferred to the parallel capacitor C p, assuming that τ1 is less than one-third of the diode reverse recovery time; Step 2.1.2, after the charge transfer is completed, the two capacitors C s and C p should have the same voltage and equivalent capacitance equal to (C s +C p ), then the charge stored in the equivalent capacitor will pass through the parallel resistor R p Discharge, in order to match the breaking characteristics of UFD, R p It should be a resistor with a large resistance so that the discharge time constant τ2 (=R p C s +R p C p ) is roughly equivalent to the UFD turn-off time. Assuming τ2 is about 400~700μs, since the UFD turn-off time is about 2ms, the LCS branch current i LCS and buffer capacitor voltage u cs For a time-varying relationship, see Figure 2 ; Step 2.2, draw the IGBT-TLCS turn-off model and the equivalent circuit of the UVRCD buffer circuit at each stage of the turn-off process, and analyze the working principle of the buffer circuit; Step 2.2.1, buffer capacitor C s The charging process, Figure 2 Where [t0, t1] is the buffer capacitor C s The charging time of the UVRCD buffer circuit is shown in the shutdown model. Figure 3 As shown in (a), when t=t0, the IGBT-TLCS starts to turn off, and the current i c The source effect of the turn-off model on the UVRCD buffer circuit can be represented by a current source id in parallel with an inductor Lp in the charging range. p >>C s And the resistor R sp The presence of the buffer capacitor C s During the charging period, the current flows through R sp With C p The current in the series branch can be ignored, so the equivalent circuit of the charging process is obtained, see Figure 3 , because R p is a large value resistor, so, Figure 3 The equivalent circuit shown in (b) is an underdamped parallel resonant circuit driven by a current source. The expression of the current source id(t) is as follows: (2-1) Where: i pis the current on the stray inductance Lp, u cs is the buffer capacitor C s voltage.

[0050] At the initial time t0, the initial current value of the inductor Lp is I p0 and buffer capacitor C s The initial voltage value U cs0 All are zero.

[0051] Capacitor voltage u cs (t) and the inductor current i p The expression of (t) is as follows: (2-2) Where: α is the damping coefficient; is the resonant frequency; is the damping frequency; is the turn-off time of IGBT-TLCS.

[0052] The expressions of the parameters in the formula are: (2-3) When t=t1, the IGBT-TLCS is completely turned off, so the fault current iLs(t1) is equal to I LST , and the voltage u on the IGBT-TLCS cs (t1) is equal to Up, less than or equal to U SSCM , U SSCM is the maximum value of the IGBT-TLCS output voltage.

[0053] Step 2.2.2, charge transfer process, Figure 2 Where [t1, t2] is the charge transfer time, and the equivalent circuit of the charge transfer interval [t1, t2] is as follows: Figure 3 (c) shown.

[0054] At time t1, C s The voltage u cs (t1) is equal to Up, the stored charge QC s for: (2-4) Because the resistor R sp The current limiting effect and C p >>C s , assuming that the capacitor C p The initial voltage value uC p (t1) is zero. And because R p >>R sp , stored in C s The charge in the resistor R sp Start the transfer to Cs p, and R p Approximately an open circuit.

[0055] Using the nodal charge conservation law, the final values ​​of the two capacitors will have the same voltage, expressed as: (2-5) It can be seen that the final voltage value is reduced ( + ) times. Assume =3 , then the capacitance The voltage on the capacitor is reduced by 4 times. for: (2-6) Equivalent Capacitance The voltage expression is: (2-7) Then the charge transfer time constant τ1 is: (2-8) According to C s The initial value iRCD (t1) and final value iRCD (∞) of the discharge current are obtained based on the three-element solution method of the first-order dynamic circuit, C s The expression of discharge current iRCD (t) is: (2-9) capacitance and The voltage expression is: (2-10) in, From the above analysis, it can be concluded that the capacitor The final voltage value is reduced ( + ) times, the charge transfer time constant τ1 is very small, so the charge transfer process is a relatively fast-changing transition process.

[0056] Step 2.2.3, capacitor discharge process, Figure 2 Where [t2, t3] is the capacitor discharge time, and the equivalent circuit of the capacitor discharge interval [t2, t3] is as follows: Figure 3 (d) shown.

[0057] When t=t2, the charge transfer process has been completed and the capacitor and Therefore, in the discharge interval, the initial value of the capacitor voltage is: (2-11) Because R p >>R sp , so it can be considered that R sp is the equivalent of an ideal wire R p Short circuit, the discharge constant τ2 is: (2-12) Equivalent capacitor voltage u ceq (t) is: (2-13).

[0058] Step 3: Regulate the buffer capacitor C based on the turn-off energy loss s Optimization, including: Step 3.1, according to the buffer capacitor C s Voltage expression, get C with different capacitance values s The corresponding IGBT voltage and current waveforms, based on the waveform curve, calculate the buffer capacitor C s The reference value C s1 ; Before turning off, the current i of the IGBT-TLCS c Equal to I LST , the output voltage is approximately zero. During the IGBT-TLCS shutdown process, the current i c With a constant (di / dt) slope, according to step 2.2.1, the buffer capacitor C s The charging interval [t0, t1], the buffer diode D s On, buffer capacitor C s Voltage u cs (t) Same as the voltage of IGBT-TLCS.

[0059] Snubber capacitor C s The voltage expression is as follows: (3-1) Where: is the current passing through the current limiting reactor Ls; is the turn-off time of IGBT-TLCS; is the stray inductance; is the shutdown start time of LCS; is the resonant frequency of the circuit.

[0060] Using Taylor's formula, equation (3-1) can be simplified to: (3-2) From formula (3-2), we can know that the turn-off voltage of IGBT-TLCS is related to the buffer capacitor C sThe capacitance value is inversely proportional to the capacitance value. s The corresponding IGBT voltage and current waveforms are as follows: Figure 4 As shown in (a), curve ① corresponds to the smaller capacitance of the buffer capacitor. It can be seen from curve ① that before the current fall time (tf) ends, the voltage of the IGBT-TLCS has risen to U SSCM , causing the IGBT-TLCS to enter the SSCM mode in advance; assuming C s =C s1 , so that the voltage u cs Just at the end of the current falling time tf, it rises to U SSCM ,u cs The waveform is shown in curve ②. Let t=tf, u cs = Usscm Substituting into formula (3-2), we can calculate : (3-3) Where: is the maximum value of the IGBT-TLCS output voltage.

[0061] Step 3.2, according to step 3.1, different capacitance values ​​of C s The corresponding IGBT voltage and current waveforms are obtained for different capacitance values ​​C s The turn-off switch trajectory curve is plotted, and the turn-off energy loss and C are plotted according to the expression of the IGBT-TLCS turn-off energy loss and the energy loss expression of the snubber circuit. s The relationship curve of the values ​​is obtained, and the buffer capacitance C s The value range of .

[0062] If the buffer capacitor C s Greater than the reference value (C s >C s1 ), u cs The waveform is as Figure 4 (a) Curve ③ shows that during the IGBT-TLCS shutdown process, the output voltage rises slowly. At the moment when the IGBT-TLCS is completely turned off, the output voltage does not reach U SSCM For three different capacitance values, the switching trajectory of the IGBT-TLCS turn-off process is shown in the figure below: Figure 4 (b) shown.

[0063] The expression of IGBT-TLCS turn-off energy loss is as follows: (3-4) Where: It is the IGBT-TLCS turn-off energy loss; is the voltage between collector and emitter when turned off.

[0064] The energy loss expression of the buffer circuit. According to the working principle of the buffer circuit, the energy stored in the buffer capacitor C s The energy can only pass through the resistor R p Consumption: (3-5) Where: for Energy loss; U p C s The peak voltage.

[0065] Plotting the turn-off energy loss vs. C s The relationship curve of the values ​​is as follows Figure 5 The horizontal axis is C s1 The capacitance ratio C s / C s1 The total vertical coordinates are IGBT-TLCS turn-off loss and energy consumption. , resistor R p Energy loss E Rp And the total energy consumption E tot Total energy consumption E tot The expression is as follows: (3-6) Depend on Figure 5 It can be seen that if C s =0.707C s1 , then EIGBT=E Rp , the total energy loss E tot tends to the minimum, as C s The gradual increase of E Rp is increasing, and It is decreasing, but the total energy loss E tot There was no significant increase.

[0066] Snubber capacitor C s The selection of should follow the following two principles: (1) Ensure that the switching trajectory of the IGBT-TLCS turn-off process is as follows: Figure 4 (b) is shown as curve ③ in order to minimize its energy dissipation; (2) the total energy loss should be kept at a low level. s The value range of is: (3-7) Step 4: According to different L p / t f i during the shutdown process under the ratio c 、u ce and i pThe waveform is analyzed and L is obtained based on the turn-off loss, peak voltage and turn-off response time. p / t f The optimal ratio of and the “slope matching criterion” are obtained, including: Step 4.1, during the IGBT-TLCS off period, based on the IGBT-TLCS collector current i c The relevant formulas for different L p / t f i during the shutdown process under the ratio c 、u ce and i p Waveform graph.

[0067] The collector current expression during the IGBT-TLCS shutdown period is: (4-1) Where: i LS is the fault current; i p is the current in the stray inductance.

[0068] From the above formula, the stray inductance L p The current i p Coupled to the gate drive voltage u ge , forming an equivalent "current-parallel negative feedback" effect, which in turn affects the IGBT-TLCS output voltage u cs . Different L p / t f The turn-off waveform under the ratio is as follows Figure 6 As shown, the shaded area represents the turn-off loss.

[0069] Step 4.2, get different L according to the waveform diagram of step 4.1 p / t f The influence of the ratio on the turn-off loss, peak voltage and turn-off response time is used to determine L p / t f The optimal ratio of is obtained and a “slope matching criterion” is proposed.

[0070] Step 4.2.1, L p / t f When the ratio is large, the main circuit breaker has a large reactance, causing the current i p With a smaller conversion rate, the IGBT-TLCS collector current i c Has a large conversion rate, resulting in i p with i c Conversion rate mismatch. At high L p / t f ratio, the main circuit breaker circuit severely restricts the switching speed of the IGBT-TLCS. Figure 6As shown in (a), the peak voltage of the IGBT-TLCS output voltage has reached the maximum value U SSCM , and there is a large turn-off loss. Therefore, for a hybrid circuit breaker without a snubber circuit, a high L p / t f The ratio is a non-ideal operating condition.

[0071] Step 4.2.2, L p / t f When the ratio is small, i p The rate of change is much greater than i c The rate of change of the shutdown waveform is as follows: Figure 6 As shown in (b), the commutation time of LCS mainly depends on the response speed of the IGBT-TLCS gate circuit and is almost unaffected by the main circuit breaker. The peak voltage of the IGBT-TLCS output voltage is lower and the turn-off loss is smaller. For the hybrid circuit breaker, the low L p / t f The ratio is an ideal situation, but it is a physically impossible condition.

[0072] Step 4.2.3, L p / t f When the ratio is moderate, the turn-off waveform is as follows Figure 6 As shown in (c), the impedance of the main circuit breaker and the response speed of the gate drive circuit are "matched" to each other, L p / t f The ratio reaches the optimal value. From formula (4-1), we can see that i p with i c There is a dynamic coupling relationship between them, so the slope matching criterion is: the main circuit breaker current i p The rising rate of change is not allowed to exceed the IGBT-TLCS collector current i c rate of decline.

[0073] In a specific embodiment of the present invention, step 5 is further included to verify the superiority of the novel unidirectional variable time constant RCD snubber circuit, which specifically includes: Step 5.1, according to the turn-off models of different snubber circuits, the voltage waveforms of the snubber circuits in the LCS commutation process of different snubber circuits are obtained, and the PSCAD / EMTDC simulation equivalent circuit is built to simulate the voltage waveforms of the active RCD snubber circuit and the new UVRCD snubber circuit in the LCS commutation process, as shown in Figure 5. Figure 7 As shown, curve ① represents the voltage waveform of the active RCD buffer circuit, and curve ② represents the simulated voltage waveform of the new UVRCD buffer circuit. Step 5.2, according to step 5.1, the voltage waveform of the buffer circuit is obtained, and the influence of different buffer circuits on the turn-off oscillation and peak voltage is compared. From curve ①, it can be seen that the active buffer circuit has the following disadvantages, such as causing singular point A, the existence of turn-off oscillation, and a peak voltage of up to 2.7kV at point B. Compared with curve ①, the new UVRCD buffer circuit eliminates the singular point A and the turn-off oscillation, and reduces the peak voltage to 2.4kV.

[0074] By comparing the voltage waveforms and parameters such as turn-off oscillation and peak voltage of different buffer circuits, the present invention verifies the superiority of the new unidirectional variable time constant RCD buffer circuit. The verification results show that the UVRCD buffer circuit provided by the present invention has advantages in improving circuit breaker performance, reducing turn-off loss and peak voltage, etc.

[0075] Compared with the active RCD snubber circuit, the new UVRCD snubber circuit retains the advantages of the active RCD snubber circuit and eliminates its disadvantages. It also has a series of advantages. The new snubber circuit adds a snubber diode, which helps to better control the reverse current and prevent the circuit from being damaged by excessive or insufficient current. At the same time, it prevents the discharge current of the snubber capacitor from flowing back through the UFD to avoid the shutdown delay of the UFD. The snubber capacitor absorbs the charge released by the switch tube during the shutdown process of the switch tube, thereby slowing down the current drop speed, reducing the current peak at shutdown, and reducing the shutdown loss, thereby improving the shutdown reliability of the hybrid DC circuit breaker. The large resistor and capacitor in parallel help to increase the discharge time constant, and the discharge branch prolongs the discharge time to eliminate the shutdown oscillation.

[0076] This embodiment also provides a chip, including the buffer circuit as described above. The chip is also called an integrated circuit (IC), and the chip can be but is not limited to a SOC (System on Chip). p , system-on-chip) chip, SIP (system in package, system-level packaging) chip. Considering that when the output voltage of the buffer circuit is small, the buffer circuit works in an environment with a small load, and the driving capability required is small, and accordingly, the current it needs to provide is small; when the output voltage of the buffer circuit is large, the buffer circuit works in an environment with a large load, and the driving capability required is large, and accordingly, the current it needs to provide is large. This chip, through the current supplement module, injects a supplementary current into the output end of the buffer module based on the output voltage of the buffer module to adjust the output current of the buffer module, so that the output current of the buffer circuit is related to the output voltage, rather than always outputting a large output current. Therefore, the embodiment of the present application can drive the load within a larger voltage range and achieve lower power consumption.

[0077] The present embodiment also includes an electronic device, including a device body and a chip as described above provided in the device body. The electronic device may be, but is not limited to, a weight scale, a body fat scale, a nutrition scale, an infrared electronic thermometer, a pulse oximeter, a human body composition analyzer, a mobile power supply, a wireless charger, a fast charger, a car charger, an adapter, a display, a USB (Universal Serial Bus) docking station, a stylus, a true wireless headset, a car central control screen, a car, a smart wearable device, a mobile terminal, and a smart home device. Smart wearable devices include, but are not limited to, smart watches, smart bracelets, and cervical massagers. Mobile terminals include, but are not limited to, smart phones, laptops, tablet computers, and POS (point of sales terminal). Smart home devices include, but are not limited to, smart sockets, smart rice cookers, smart sweepers, and smart lights. Considering that when the output voltage of the buffer circuit is small, the buffer circuit works in an environment with a small load, and the driving capacity required is small, and accordingly, the current it needs to provide is small; when the output voltage of the buffer circuit is large, the buffer circuit works in an environment with a large load, and the driving capacity required is large, and accordingly, the current it needs to provide is large. The electronic device injects a supplementary current into the output end of the buffer module based on the output voltage of the buffer module through a current supplement module to adjust the output current of the buffer module, so that the output current of the buffer circuit is related to the output voltage, rather than always outputting a larger output current. Therefore, the embodiment of the present application can drive the load within a larger voltage range and achieve lower power consumption.

[0078] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A snubber circuit suitable for a hybrid DC circuit breaker, characterized in that: Including snubber diode D s , buffer capacitor C s , large capacity capacitor C p , small resistance resistor R sp And the large resistance R p ; Snubber diode D s The first branch is connected in parallel with the first branch, the second branch and the third branch respectively. The first branch is the charging branch, which consists of a buffer capacitor C s The second branch is the charge transfer branch, which consists of a large-capacity capacitor C p Connect a small resistance R in series sp The third branch is the discharge branch, which consists of a large resistance resistor R p constitute; When applied, the snubber circuit is connected in parallel to the load transfer switch IGBT-TLCS of the hybrid DC circuit breaker.

2. A method for optimizing snubber circuit parameters for a hybrid DC circuit breaker, characterized in that: The snubber circuit for a hybrid DC circuit breaker according to claim 1 comprises the following steps: S1. Topological structure when constructing buffer circuit application; S2. Based on the topology, draw the LCS branch current i of the hybrid DC circuit breaker LCS and buffer capacitor C s The voltage u cs A relationship curve that changes with time; based on the relationship curve, a turn-off model of the load transfer switch IGBT-TLCS is constructed, and according to the turn-off model, an equivalent circuit of the buffer circuit at different stages of the turn-off process is obtained, wherein the turn-off process includes three stages: charging process, charge transfer process and capacitor discharge process; S3. Analyze the working principle of the buffer circuit at different stages of the shutdown process and construct the buffer capacitor C s The voltage expression of and the turn-off energy loss expression of the load transfer switch IGBT-TLCS; Based on the voltage expression, plot the buffer capacitor C with different capacitance values s Calculate the snubber capacitor C according to the voltage and current waveforms and switch trajectory of the load transfer switch IGBT-TLCS s The reference value C s1 ; Based on the voltage expression and the turn-off energy loss expression, plot the turn-off energy loss versus the snubber capacitance C s The relationship curve, combined with the reference value C s1 , get the buffer capacitor C s The optimal value range of .

3. A method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 2, characterized in that: It also includes S4, according to the shutdown model, the collector current of the load transfer switch IGBT-TLCS is analyzed The expression is: Among them, i LS is the fault current; i p is the current of stray inductance; According to the collector current The expression of stray inductance L of different hybrid DC circuit breakers is p The turn-off time t of the load transfer switch IGBT-TLCS f The collector current i during the turn-off process is plotted under the ratio of c 、The voltage u between the collector and emitter of IGBT-TLCS ce and stray inductor current i p Waveform graph; Analyze the waveform diagram to obtain different L p / t f The influence of the ratio on the turn-off loss, peak voltage and turn-off response time is used to determine L p / t f Based on the optimal ratio, the stray inductance current i is obtained. p With the collector current i c The slope matches the relationship.

4. The method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 2, characterized in that: Snubber capacitor C s The voltage expression is as follows: The buffer capacitor C s The charging process [t0, t1], Among them, α is the damping coefficient; is the resonant frequency; is the damping frequency; is the turn-off time of the load transfer switch IGBT-TLCS, is the peak current of the current source equivalent to the snubber circuit in the turn-off model, is the buffer capacitor C s The charging process starts at t1, and t2 is the buffer capacitor C s The end time of the charging process; The buffer capacitor C s The charge transfer process [t1, t2], in, The buffer capacitor C at time t1 s The stored charge, τ1 is the charge transfer time constant; t2 is the buffer capacitance C s The end time of the charge transfer process; The buffer capacitor C s The capacitor discharge process [t2, t3], Where τ2 is the discharge constant, is the buffer capacitor C s The peak voltage of the buffer capacitor C s The capacitor discharge process ends time.

5. A method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 4, characterized in that: The charge transfer time constant τ1 is specifically: 。 6. A method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 4, characterized in that: The discharge constant τ2 is specifically: 。 7. The method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 2, characterized in that: The turn-off energy loss expression of the load transfer switch IGBT-TLCS is as follows: in, is the turn-off energy loss of the load transfer switch IGBT-TLCS; It is the voltage between the collector and the emitter when the load transfer switch IGBT-TLCS is turned off; is the collector current; I LST At time t1, the current through the current limiting reactor L s The current; is the damping frequency; is the energy loss value; is the collector current angle of the load transfer switch IGBT-TLCS during the turn-off process; is the turn-off time of the load transfer switch IGBT-TLCS; is the buffer capacitor C s The charging process starts at t1, and t2 is the buffer capacitor C s The charging process ends at the time.

8. The method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 2, characterized in that: Snubber capacitor C s The reference value C s1 Specifically: in, is the maximum value of the output voltage of the load transfer switch IGBT-TLCS; is the turn-off time of the load transfer switch IGBT-TLCS; At time t1, the current through the current limiting reactor L s The current; The optimal value range of the buffer capacitor Cs is: 。 9. A chip, characterized in that: Comprising the buffer circuit as claimed in claim 1.

10. An electronic device, characterized in that: The device comprises a device body and a chip as claimed in claim 9 arranged in the device body.

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