A snubber circuit, method and related device suitable for a hybrid DC circuit breaker

Abstract

The application discloses a buffer circuit, a method and related equipment suitable for a hybrid DC circuit breaker, and belongs to the technical field of the hybrid DC circuit breaker. By arranging a buffer diode, the discharge current of a buffer capacitor is prevented from flowing reversely through a UFD, and the turn-off delay of the UFD is avoided; the parallel connection of the buffer diode and a charging branch enables the charging voltage of the buffer capacitor to increase slowly, reduces the turn-off loss, and thus improves the turn-off reliability of the hybrid DC circuit breaker; the parallel connection of the buffer diode and a charge transfer branch can quickly transfer the energy stored in the buffer capacitor to a large-capacity capacitor after commutation, avoids the obstruction of the buffer capacitor to the fast starting action of the UFD, and meanwhile, the introduction of a small-resistance resistor reduces the energy loss in the charge transfer process, and ensures the rapidity and high efficiency of the charge transfer; the parallel connection of the buffer diode and a discharge branch is used for controlling the discharge speed of the buffer capacitor, and thus the stable operation of the circuit is maintained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hybrid DC circuit breaker, and particularly relates to a buffer circuit of a hybrid DC circuit breaker. BACKGROUND

[0002] In recent years, with the evolution of flexible DC power transmission technology from a multi-terminal system to a DC power grid, more stringent requirements are put forward for the reliability, operational stability and safety of the power grid. According to the redundancy design principle of the power grid, the power grid must have the ability to isolate the fault line, that is, when a single line fails, the fault line can be quickly cut off and isolated to avoid causing major accidents of the whole grid. Therefore, short-circuit fault protection technology has become a key problem to be solved in the field of flexible DC power grid.

[0003] In practical applications, the combination of a DC reactor and a hybrid DC circuit breaker is considered as an effective solution for short-circuit protection of a flexible DC power grid. However, with the increase of the voltage level of the power grid, the cost of the hybrid DC circuit breaker increases sharply, and the design difficulty also increases. At the same time, the performance of the existing reactor has been difficult to meet the needs of the high-voltage DC power grid. Therefore, reducing the cost and design requirements of the hybrid DC circuit breaker and exploring new short-circuit fault current limiting technology have become core problems to be solved in the field of short-circuit fault protection of high-voltage flexible DC power grid.

[0004] In the design of the hybrid DC circuit breaker, the normal branch is an indispensable important component, which is composed 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 the fault often occurs during the LCS branch commutation. Although the traditional RCD buffer circuit can improve the reliability of the LCS to some 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 quickly opened, the capacitor in the RCD buffer circuit may still be in the charging or discharging state. If the capacitor is charging at this time, it will absorb current from the power supply, which may slow down the opening speed of the UFD, because part of the current is used to charge the capacitor instead of driving the opening of the UFD; and if the capacitor is discharging, it may release the stored charge through the resistor, which also consumes part of the current, thereby affecting the rapid opening of the UFD.

[0005] Therefore, how to design a new type of buffer circuit that can improve the reliability of the load transfer switch during the LCS branch commutation without affecting the rapid opening of the UFD has become a technical problem to be solved by the current technical personnel in the field. SUMMARY

[0006] The application aims to provide a buffer circuit, a method and related equipment suitable for a hybrid DC circuit breaker, aiming to solve the problem of hindering the fast opening operation of the UFD when the traditional RCD buffer circuit is used to improve the reliability of the hybrid DC circuit breaker.

[0007] The application solves the above technical problems by the following technical solutions:

[0008] A buffer circuit suitable for a hybrid DC circuit breaker comprises a buffer diode D s , a buffer capacitor C s , a large-capacity capacitor C p , a small-resistance resistor R sp , and a large-resistance resistor R p .

[0009] The buffer diode D s is connected in parallel with the first branch, the second branch and the third branch respectively, the first branch is a charging branch and is composed of the buffer capacitor C s , the second branch is a charge transfer branch and is composed of the large-capacity capacitor C p in series with the small-resistance resistor R sp , and the third branch is a discharging branch and is composed of the large-resistance resistor R p .

[0010] In application, the buffer circuit is connected in parallel with the load transfer switch IGBT-TLCS of the hybrid DC circuit breaker.

[0011] A buffer circuit parameter optimization method suitable for a hybrid DC circuit breaker adopts the above buffer circuit suitable for a hybrid DC circuit breaker and comprises the following steps:

[0012] S1, a topology structure of the buffer circuit in application is constructed;

[0013] S2, based on the topology structure, a relationship curve of the current i LCS of the LCS branch of the hybrid DC circuit breaker and the voltage u s of the buffer capacitor C cs changing with time is drawn, a turn-off model of the load transfer switch IGBT-TLCS is constructed based on the relationship curve, and an equivalent circuit of the buffer circuit at different stages of the turn-off process is obtained according to the turn-off model, wherein the turn-off process comprises three stages of a charging process, a charge transfer process and a capacitor discharging process;

[0014] S3, the working principle of the buffer circuit at different stages of the turn-off process is analyzed, and an expression of the voltage of the buffer capacitor C s and an expression of the turn-off energy loss of the load transfer switch IGBT-TLCS are constructed.

[0015] Based on the voltage expression, plot the snubber capacitor C with different capacitance values. s Calculate the snubber capacitor C based on the voltage and current waveforms and switching trajectory of the load transfer switch IGBT-TLCS. s The reference value C s1 ;

[0016] 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 .

[0017] The present invention is further improved in that: it also includes S4, according to the shutdown model, analyzing the collector current of the load transfer switch IGBT-TLCS The expression is:

[0018]

[0019] Among them, i LS is the fault current; i p is the current of stray inductance;

[0020] According to the collector current The expression of stray inductance L of different hybrid DC circuit breakers is p and 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;

[0021] 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 the 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 matching relationship.

[0022] A further improvement of the present invention is that the buffer capacitor C s The voltage expression is as follows:

[0023] The buffer capacitor C s The charging process [t0, t1],

[0024]

[0025] wherein, alpha is damping coefficient; is resonance frequency; is damping frequency; is turn-off time of load transfer switch IGBT-TLCS, is peak current of current source equivalent to buffer circuit in turn-off model, is charging process start time of buffer capacitor C s , t1 is charging process end time of buffer capacitor C s ;

[0026] in charge transfer process [t1, t2] of buffer capacitor C s ,

[0027]

[0028] wherein, is charge stored in buffer capacitor C s at t1, tau1 is charge transfer time constant; t2 is charge transfer process end time of buffer capacitor C s ;

[0029] in capacitor discharge process [t2, t3] of buffer capacitor C s ,

[0030]

[0031] wherein, tau2 is discharge constant, is peak voltage of buffer capacitor C s ; t3 is capacitor discharge process end time of buffer capacitor C s .

[0032] The further improvement of the present application is that the charge transfer time constant tau1 is specifically:

[0033]

[0034] The further improvement of the present application is that the discharge constant tau2 is specifically:

[0035]

[0036] The further improvement of the present application is that the turn-off energy loss expression of load transfer switch IGBT-TLCS is specifically:

[0037]

[0038] wherein, is turn-off energy loss of load transfer switch IGBT-TLCS; The voltage between the collector and emitter when the load transfer switch IGBT-TLCS is turned off; is the collector current; I LST The current through the current limiting reactor L at time t1 s 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 the buffer capacitor C s The charging process ends at the time.

[0039] A further improvement of the present invention is that the buffer capacitor C s The reference value C s1 Specifically:

[0040]

[0041] 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; The current through the current limiting reactor L at time t1 s Current;

[0042] The optimal value range of the snubber capacitor Cs is:

[0043]

[0044] A chip includes the buffer circuit as described above.

[0045] An electronic device includes a device body and a chip as described above disposed in the device body. Compared with the prior art, the present invention has the following positive improvements:

[0046] The application provides a buffer circuit suitable for a hybrid DC circuit breaker, improves the turn-off reliability of a load transfer switch, and ensures the stability and fast turn-off during commutation. By arranging a buffer diode, the discharge current of the buffer capacitor is prevented from flowing reversely through the UFD, and the turn-off delay of the UFD is avoided; the parallel connection of the buffer diode and the charging branch enables the charging voltage of the buffer capacitor to increase slowly, reduces the turn-off loss, and thus improves the turn-off 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, avoids the hindering of the buffer capacitor to the fast starting action of the UFD, and the introduction of the small-resistance resistor reduces the energy loss in the charge transfer process, and ensures the rapidity and efficiency of the charge transfer; the parallel connection of the buffer diode and the discharge branch is used for controlling the discharge speed of the buffer capacitor, and thus the stable operation of the circuit is maintained.

[0047] Further, the application provides a buffer circuit parameter optimization method suitable for a hybrid DC circuit breaker, by constructing a turn-off model, drawing a relationship curve and analyzing the working principle, the optimal value range of the buffer capacitor is obtained, which not only can improve the performance of the hybrid DC circuit breaker, but also can ensure that the circuit breaker can maintain stable fault protection ability under different working conditions.

[0048] Further, by analyzing the i p / t f , u c and i ce waveform graphs in the turn-off process under different L p / t p , the optimal ratio of L f / t is obtained, which is helpful to further optimize the design of the hybrid DC circuit breaker and improve the stability and reliability thereof in the turn-off process. BRIEF DESCRIPTION OF DRAWINGS

[0049] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the application. The schematic embodiments of the application and the descriptions thereof are used to explain the application, and do not constitute an improper limitation on the application.

[0050] Figure 1 is a turn-off model diagram containing a buffer circuit;

[0051] Figure 2 is a relationship curve of the current iLCS of the LCS branch of the hybrid DC circuit breaker and the voltage ucs of the buffer capacitor Cs with time, wherein, Fig. (a) is a relationship curve of the current iLCS, and Fig. (b) is a relationship curve of the voltage ucs;

[0052] Figure 3is the equivalent circuit of the turn-off model of the load transfer switch IGBT-TLCS and the buffer circuit in 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;

[0053] Figure 4 is the voltage, current waveform diagram and switch trajectory diagram of the load transfer switch IGBT-TLCS corresponding to the buffer capacitor Cs of different capacitance values, wherein, figure (a) is the voltage, current waveform diagram of the load transfer switch IGBT-TLCS corresponding to the buffer capacitor Cs of different capacitance values, and figure (b) is the switch trajectory diagram;

[0054] Figure 5 is the relationship curve of turn-off energy loss and buffer capacitor Cs;

[0055] Figure 6 is the turn-off waveform diagram under different Lp / tf ratios, wherein, figure (a) is the turn-off waveform diagram with a larger Lp / tf ratio, figure (b) is the turn-off waveform diagram with a smaller Lp / tf ratio, and figure (c) is the turn-off waveform diagram with a moderate Lp / tf ratio;

[0056] Figure 7 is the voltage waveform diagram of the active RCD buffer circuit and the buffer circuit in the LCS branch commutation process. DETAILED DESCRIPTION

[0057] The application will be further described in detail below in combination with the drawings and specific embodiments, which are an explanation but not a limitation of the application.

[0058] Referring to Figure 1 , the application provides a buffer circuit suitable for a hybrid DC circuit breaker, which comprises a buffer diode D s , a buffer capacitor C s , a large-capacity capacitor C p , a small-resistance resistor R sp , and a large-resistance resistor R p .

[0059] The buffer diode D s is connected in parallel with the first branch, the second branch and the third branch respectively, the first branch is a charging branch composed of the buffer capacitor C s , the second branch is a charge transfer branch composed of the large-capacity capacitor C p in series with the small-resistance resistor R sp , and the third branch is a discharge branch composed of the large-resistance resistor R p .

[0060] When applied, the snubber circuit is connected in parallel to the load transfer switch IGBT-TLCS of the hybrid DC circuit breaker.

[0061] By providing a snubber diode, the discharge current of the snubber capacitor is prevented from flowing back through the UFD, thereby avoiding a shutdown delay of the UFD. The snubber diode is connected in parallel with the charging branch, which causes the charging voltage of the snubber capacitor to increase slowly, reducing shutdown losses and thus improving the shutdown reliability of the hybrid DC circuit breaker. The snubber diode is connected in parallel with the charge transfer branch, which can quickly transfer the energy stored in the snubber capacitor to the large-capacity capacitor after commutation, thereby preventing the snubber capacitor from hindering the rapid opening of the UFD. At the same time, the introduction of a small-resistance resistor reduces energy loss during the charge transfer process, ensuring the rapidity and efficiency of the charge transfer. The snubber diode is connected in parallel with the discharge branch to control the discharge speed of the snubber capacitor, thereby maintaining stable operation of the circuit.

[0062] The present invention further provides a method for optimizing parameters of a snubber circuit applicable to a hybrid DC circuit breaker, which uses the snubber circuit applicable to the hybrid DC circuit breaker, and includes the following steps:

[0063] S1. Topology structure when constructing buffer circuit application;

[0064] 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 snubber 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;

[0065] 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;

[0066] Based on the voltage expression, plot the snubber capacitor C with different capacitance values. s Calculate the snubber capacitor C based on the voltage and current waveforms and switching trajectory of the load transfer switch IGBT-TLCS. s The reference value C s1 ;

[0067] 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 sThe optimal value range of .

[0068] By constructing a shutdown model, drawing relationship curves, and analyzing the working principle, the optimal value range of the snubber capacitor was obtained. This not only improves the performance of the hybrid DC circuit breaker, but also ensures that the circuit breaker maintains stable fault protection capabilities under different operating conditions.

[0069] Specifically, it also includes S4, according to the shutdown model, analyzing the collector current of the load transfer switch IGBT-TLCS The expression is:

[0070]

[0071] Among them, i LS is the fault current; i p is the current of stray inductance;

[0072] According to the collector current The expression of stray inductance L of different hybrid DC circuit breakers is p and 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;

[0073] 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 the 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 matching relationship.

[0074] By analyzing different L p / t f i during the shutdown process under the ratio c 、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.

[0075] Specifically, the buffer capacitor C s The voltage expression is as follows:

[0076] The buffer capacitor Cs charging process of the buffer capacitor C

[0077]

[0078] wherein, α is a damping coefficient; is a resonance frequency; is a 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 buffer circuit in the turn-off model, is the peak voltage of the buffer capacitor C s , t1 is the end time of the charging process of the buffer capacitor C s ;

[0079] in the charge transfer process of the buffer capacitor C s [t1, t2],

[0080]

[0081] wherein, is the charge stored in the buffer capacitor C s at t1, τ1 is a charge transfer time constant; t2 is the end time of the charge transfer process of the buffer capacitor C s ;

[0082] in the capacitor discharge process of the buffer capacitor C s [t2, t3],

[0083]

[0084] wherein, τ2 is a discharge constant, is the peak voltage of the buffer capacitor C s ; t3 is the end time of the capacitor discharge process of the buffer capacitor C s ;

[0085] Specifically, the charge transfer time constant τ1 is specifically:

[0086] .

[0087] Specifically, the discharge constant τ2 is specifically:

[0088] .

[0089] Specifically, the turn-off energy loss expression of the load transfer switch IGBT-TLCS is specifically:

[0090]

[0091] wherein, is the turn-off energy loss of the load transfer switch IGBT-TLCS; The voltage between the collector and emitter when the load transfer switch IGBT-TLCS is turned off; is the collector current; I LST The current through the current limiting reactor L at time t1 s 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 the buffer capacitor C s The charging process ends at the time.

[0092] Specifically, the buffer capacitor C s The reference value C s1 Specifically:

[0093]

[0094] 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; The current through the current limiting reactor L at time t1 s of current.

[0095] The optimal value range of the snubber capacitor Cs is:

[0096] .

[0097] In a specific embodiment of the present invention, a method for optimizing snubber circuit parameters for a hybrid DC circuit breaker is provided, which is specifically implemented according to the following steps:

[0098] Step 1: Construct a novel unidirectional variable time constant RCD (UVRCD) snubber circuit topology, specifically including:

[0099] Step 1.1, the new unidirectional variable time constant RCD snubber circuit includes a snubber diode D s , buffer capacitor C s , large-capacity capacitor C p , small resistor R sp , large resistor R p ;

[0100] Step 1.2, the topology of UVRCD buffer circuit is constructed, see Figure 1 , buffer diode D s is connected in parallel with three branches, the three parallel branches are respectively: ① a charging branch composed of buffer capacitor C s ; ② a charge transfer branch composed of a large capacity capacitor C p in series with a small resistance R sp ; ③ a discharging branch composed of a large resistance R p . Among them, the buffer diode D s can effectively prevent the discharge current of C s from flowing reversely through the UFD, avoiding the delay of UFD turn-off, and achieving the purpose of reducing the peak value of fault current; during the turn-off of IGBT-TLCS, the slow growth of the charging voltage of buffer capacitor C s effectively reduces the rising rate of the turn-off voltage of IGBT-TLCS, greatly reducing the turn-off loss.

[0101] Step 2, according to the topology of the new one-way-variable time constant RCD buffer circuit established in step 1, the main waveform diagram is drawn, and the working principle is analyzed according to the equivalent circuit of each stage during the turn-off process of IGBT-TLCS, which specifically includes:

[0102] Step 2.1, according to the new one-way-variable time constant RCD (UVRCD) buffer circuit established in step 1, the relationship curves of the current i LCS of the LCS branch and the voltage u cs of the buffer capacitor changing with time are drawn;

[0103] Step 2.1.1, after the fault current is completely commutated from the LCS branch to the main circuit breaker branch, the current i LCS is equal to zero, and the current i p is equal to the current i s flowing through the current limiting reactor L LS . Since 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, the UVRCD buffer circuit is isolated from the original circuit due to the turn-off of the UFD and the existence of the buffer diode D s , becoming an isolated circuit. In this isolated circuit, because R sp is about 10Ω, which is very small, resulting in a very small time constant τ1 (=R sp C s +R sp C p ), so the charge stored in the capacitor C s will be quickly transferred to the parallel capacitor C sp through R p, assuming that τ1 is less than one-third of the diode reverse recovery time;

[0104] Step 2.1.2, after the charge transfer is completed, the two capacitors C s and C p should have the same voltage, 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 that 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 the time-varying relationship curve, see Figure 2 ;

[0105] Step 2.2: Draw the IGBT-TLCS turn-off model and the equivalent circuit of the UVRCD snubber circuit at each stage of the turn-off process, and analyze the working principle of the snubber circuit;

[0106] 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 snubber 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 shutdown model on the UVRCD snubber circuit can be represented by a current source id in parallel with an inductor Lp in the charging range. p >>C s and resistor R sp The presence of the buffer capacitor C s During the charging period, the current flowing 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:

[0107] (2-1)

[0108] where i p is the current on the stray inductance Lp, u cs is the voltage on the buffer capacitor C s .

[0109] At the initial time t0, the initial value of the current i p0 on the inductance Lp and the initial value of the voltage u s on the buffer capacitor C cs0 are both zero.

[0110] The expression of the capacitor voltage u cs (t) and the inductance current i p (t) is as follows:

[0111] (2-2)

[0112] where α is the damping coefficient; ω0is the resonance frequency; ωdis the damping frequency; and t is the turn-off time of the IGBT-TLCS. The expression of each parameter is as follows:

[0113]

[0114] (2-3)

[0115] 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 cs (t1) on the IGBT-TLCS is equal to Up, which is less than or equal to U SSCM , and U SSCM is the maximum value of the output voltage of the IGBT-TLCS.

[0116] 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 shown in Figure 3 (c).

[0117] At the time t1, the voltage u s (t1) on the capacitor C cs is equal to Up, and the stored charge QC s is:

[0118] (2-4)

[0119] Because of the current-limiting effect of the resistor R sp and the charge transfer of the capacitor C​​p >>C s The voltage initial value uC p of the capacitor C p (t1) is zero. Again because R p >>R sp The charge stored in C s will start to transfer to C sp through the resistance R s p, and R p is approximately open circuit.

[0120] Using the node charge conservation law, the final values of the two capacitors will have the same voltage, denoted as:

[0121] (2-5)

[0122] It can be seen that the final voltage value is reduced by (1+R + ) times. Assuming =3 , the voltage on the capacitor C is reduced by 4 times. At this time, the equivalent capacitor C is:

[0123] (2-6)

[0124] The voltage expression of the equivalent capacitor C is:

[0125] (2-7)

[0126] The charge transfer time constant τ1 is:

[0127] (2-8)

[0128] According to the initial value iRCD (t1) and the final value iRCD (∞) of the discharge current of C s , the expression of the discharge current iRCD (t) of C s is obtained based on the three-element solution method of first-order dynamic circuits:

[0129] (2-9)

[0130] The voltage expressions of the capacitors C and C are:

[0131] (2-10)

[0132] wherein , from the above analysis, the capacitor C The final voltage value of the capacitor is reduced by + ) times, and the charge transfer time constant τ1 is very small, so the charge transfer process is a relatively fast transition process.

[0133] Step 2.2.3, capacitor discharge process, Figure 2 The capacitor discharge time interval [t2, t3] is shown in Figure 3 (d).

[0134] When t = t2, the charge transfer process is completed, and the capacitor and share the same voltage. Therefore, in the discharge interval, the initial value of the capacitor voltage is:

[0135] (2-11)

[0136] Because R p >>R sp , it can be considered that R sp is an equivalent ideal wire that short-circuits R p , and the discharge constant τ2 is:

[0137] (2-12)

[0138] The equivalent capacitor voltage u ceq (t) is:

[0139] (2-13).

[0140] Step 3, optimize the buffer capacitor C s based on the turn-off energy loss, which specifically includes:

[0141] Step 3.1, according to the buffer capacitor C s voltage expression, get the corresponding IGBT voltage and current waveform of C s of different capacitance value, according to the waveform curve to calculate the reference value C s of the buffer capacitor C s1 ;

[0142] Before turn-off, the current i c of IGBT-TLCS is equal to I LST , and the output approximate voltage is zero. During the turn-off process of IGBT-TLCS, the current i c drops at a constant (di / dt) slope. According to step 2.2.1, in the charging interval [t0, t1] of the buffer capacitor C s , the buffer diode D s is turned on, and the buffer capacitor Cs Voltage u cs (t) is the same as the voltage of IGBT-TLCS.

[0143] Snubber capacitor C s The voltage expression is as follows:

[0144] (3-1)

[0145] 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.

[0146] Using Taylor's formula, we can simplify equation (3-1) to:

[0147] (3-2)

[0148] From formula (3-2), we can know that the turn-off voltage of IGBT-TLCS is related to the buffer capacitor C s The 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 snubber 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, t=tf, u cs = Usscm Substituting into formula (3-2), we can calculate :

[0149] (3-3)

[0150] Where: is the maximum value of the IGBT-TLCS output voltage.

[0151] 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 sThe turn-off switch trajectory curve is plotted, and the turn-off energy loss and C are plotted based on 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 .

[0152] 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)

[0153] The expression of IGBT-TLCS turn-off energy loss is as follows:

[0154] (3-4)

[0155] Where: IGBT-TLCS turn-off energy loss; is the voltage between the collector and emitter when the device is turned off.

[0156] The energy loss expression of the snubber circuit. According to the working principle of the snubber circuit, the energy stored in the snubber capacitor C s The energy can only pass through the resistor R p Consumption:

[0157] (3-5)

[0158] Where: for Energy loss; U p C s The peak voltage.

[0159] Plotting the turn-off energy loss vs. C s The relationship curve of the values ​​is as follows Figure 5 As shown. The horizontal axis is C s1 The capacitance ratio C is the reference value s / C s1 The total vertical axis is IGBT-TLCS turn-off loss energy consumption , resistor R p Energy loss E Rp And the total energy consumption E tot Total energy consumption E totThe expression is as follows:

[0160] (3-6)

[0161] 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 Increasing, and It is decreasing, but the total energy loss E tot There was no significant increase.

[0162] 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 as much as possible. s The value range of is:

[0163] (3-7)

[0164] Step 4: According to different L p / t f i during the shutdown process under the ratio c 、u ce and i p The 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, which include:

[0165] 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.

[0166] The collector current expression during the IGBT-TLCS turn-off period is:

[0167] (4-1)

[0168] Where: i LS is the fault current; i pcurrent on the stray inductance.

[0169] From the above equation, the stray inductance L p The current i p is 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 ratios result in different turn-off waveforms, as shown in Fig. Figure 6 The shaded part represents the turn-off loss.

[0170] Step 4.2, according to the waveform diagram of step 4.1, the influence of different L p / t f ratios on the turn-off loss, peak voltage, and turn-off response time is determined, the optimal L p / t f ratio is determined, and the "slope matching criterion" is proposed.

[0171] Step 4.2.1, when the L p / t f ratio is large, the main circuit has a large reactance, resulting in a small transformation rate of the current i p , a large transformation rate of the IGBT-TLCS collector current i c , and a mismatch between i p and i c . At high L p / t f ratios, the main circuit severely restricts the switching speed of the IGBT-TLCS, as shown in Fig. Figure 6 (a), the peak voltage of the IGBT-TLCS output voltage has reached the maximum U SSCM , and there is a large turn-off loss. Therefore, for a hybrid circuit without a buffer circuit, high L p / t f ratios are an undesirable working condition.

[0172] Step 4.2.2, when the L p / t f ratio is small, the change rate of i p is much larger than that of i c , and the turn-off waveform is shown in Fig. Figure 6 (b), the commutation time of the LCS is mainly determined by the response speed of the IGBT-TLCS gate circuit, and is almost unaffected by the main circuit, the peak voltage of the IGBT-TLCS output voltage is low, and the turn-off loss is small, for a hybrid circuit, low L p / t fThe ratio is an ideal situation, but it is a physically impossible working condition.

[0173] 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 descent.

[0174] 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, specifically comprising:

[0175] In step 5.1, according to the turn-off models of different snubber circuits, the voltage waveforms of the snubber circuits during the LCS commutation process of different snubber circuits are obtained. A PSCAD / EMTDC simulation equivalent circuit is built to simulate the voltage waveforms of the active RCD snubber circuit and the new UVRCD snubber circuit during the LCS commutation process, as shown in Figure 5. Figure 7 As shown, curve ① represents the voltage waveform of the active RCD snubber circuit, and curve ② represents the simulated voltage waveform of the new UVRCD snubber circuit.

[0176] Step 5.2: Obtain the voltage waveform of the buffer circuit according to step 5.1, and compare the effects of different buffer circuits on the turn-off oscillation and peak voltage. As can be seen from curve ①, 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 2.7 kV at point B. Compared with curve ①, the new UVRCD buffer circuit eliminates singular point A and turn-off oscillation, and reduces the peak voltage to 2.4 kV.

[0177] By comparing the voltage waveforms and parameters such as turn-off oscillation and peak voltage of different snubber circuits, the present invention verifies the superiority of the new unidirectional-variable time constant RCD snubber circuit. The verification results show that the UVRCD snubber circuit provided by the present invention has advantages in improving circuit breaker performance, reducing turn-off loss and peak voltage, etc.

[0178] Compared with the active RCD snubber circuit, the new UVRCD snubber circuit retains the advantages of the active RCD snubber circuit while eliminating its disadvantages. It also offers a range of advantages. The addition of a snubber diode in the new snubber circuit helps better control reverse current, preventing damage to the circuit caused by excessive or insufficient current. It also prevents the discharge current of the snubber capacitor from flowing back through the UFD, avoiding UFD shutdown delays. The snubber capacitor absorbs the charge released by the switch during its shutdown, thereby slowing the current drop rate, reducing the current peak during shutdown, and minimizing shutdown losses, thereby improving the shutdown reliability of the hybrid DC circuit breaker. The parallel connection of a large resistor and capacitor helps increase the discharge time constant. The discharge branch prolongs the discharge time and eliminates shutdown oscillations.

[0179] This embodiment also provides a chip, including the buffer circuit as described above. The chip is also called an integrated circuit (IC), which can be but 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 relatively low, the buffer circuit operates in an environment with a relatively small load, and the driving capability required is relatively low, and accordingly, the current required to be provided is relatively small; when the output voltage of the buffer circuit is relatively high, the buffer circuit operates in an environment with a relatively large load, and the driving capability required is relatively high, and accordingly, the current required to be provided is relatively high. This chip, through a 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 relatively large output current. Therefore, the embodiment of the present application can drive the load within a relatively large voltage range and achieve relatively low power consumption.

[0180] The embodiment also includes an electronic device including a device body and the chip as described above arranged on the device body. The electronic device can be, but is not limited to, a body 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 vehicle charger, an adapter, a display, a USB (Universal Serial Bus) docking station, a touch pen, a true wireless earphone, a car central control screen, a car, a smart wearable device, a mobile terminal, and a smart home device. The smart wearable device includes, but is not limited to, a smart watch, a smart bracelet, and a cervical vertebra massage instrument. The mobile terminal includes, but is not limited to, a smart phone, a notebook computer, a tablet computer, and a POS (point of sale terminal) machine. The smart home device includes, but is not limited to, a smart socket, a smart rice cooker, a smart sweeper, and a smart lamp. Considering that the buffer circuit works in a small load environment when the output voltage of the buffer circuit is small, the driving capability required by the buffer circuit is small, and accordingly, the current required to be provided by the buffer circuit is small; when the output voltage of the buffer circuit is large, the buffer circuit works in a large load environment, the driving capability required by the buffer circuit is large, and accordingly, the current required to be provided by the buffer circuit is large. The electronic device injects a supplementary current to the output end of the buffer module based on the output voltage of the buffer module through the current supplement module, so as 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. Thus, the embodiment of the present application can drive the load in a large voltage range and achieve small power consumption.

[0181] The above merely describes the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical solution falls within the protection scope of the present application.

Claims

1. A method for optimizing snubber circuit parameters for a hybrid DC circuit breaker, characterized in that: Snubber circuit for hybrid DC circuit breaker, including snubber diode D s , buffer capacitor C s , large-capacity capacitor C p , small resistance resistor R sp And the large resistance resistor R p ; Snubber diode D s The first branch is connected in series with the first branch, the second branch and the third branch in parallel. The first branch is the charging branch, which is composed 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 resistor R in series sp The third branch is the discharge branch, which consists of a large resistance resistor R p constitute; When used, the snubber circuit is connected in parallel to the load transfer switch IGBT-TLCS of the hybrid DC circuit breaker; A method for optimizing snubber circuit parameters for a hybrid DC circuit breaker includes the following steps: S1. Topology 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 snubber 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 snubber capacitor C with different capacitance values. s Calculate the snubber capacitor C based on the voltage and current waveforms and switching 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 ; 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; The current through the current limiting reactor L at time t1 s Current; The optimal value range of the snubber capacitor Cs is: It also includes S4, according to the turn-off 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 and 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 the 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 matching relationship.

2. The method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 1, characterized in that: Snubber capacitor C s The voltage expression is as follows: The buffer capacitor C s The charging process [t0, t1], Where 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 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 end time of the capacitor discharge process.

3. The method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 2, wherein: The charge transfer time constant τ1 is specifically: 。 4. The method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 2, wherein: The discharge constant τ2 is specifically: 。 5. The method for optimizing snubber circuit parameters for a hybrid DC circuit breaker according to claim 1, characterized in that: The turn-off energy loss expression of the load transfer switch IGBT-TLCS is: in, is the turn-off energy loss of the load transfer switch IGBT-TLCS; The voltage between the collector and emitter when the load transfer switch IGBT-TLCS is turned off; is the collector current; I LST The current through the current limiting reactor L at time t1 s 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 the buffer capacitor C s The charging process ends at the time.

6. A chip, characterized in that: The method comprises the buffer circuit of the buffer circuit parameter optimization method applicable to the hybrid DC circuit breaker as claimed in claim 1.

7. An electronic device, characterized in that: The device comprises a device body and the chip according to claim 6 arranged in the device body.

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