Modeling Method and Application of a Load Commutated Switch for a High-Voltage Hybrid DC Circuit Breaker

Abstract

The present invention discloses a modeling method and application of a load-commutated switch of a high-voltage hybrid DC circuit breaker, belonging to the technical field of DC circuit breakers. By constructing a simplified principle model of the high-voltage hybrid DC circuit breaker and combining an accurate soft turn-through power electronic switch turn-off analysis model under extreme safe operating area conditions, a complete load-commutated switch turn-off equivalent circuit is established; by setting the action timing diagram, the IGBT current-limiting mechanism of the main circuit breaker branch in the high-voltage hybrid DC circuit breaker is revealed, and its dynamic characteristics during the load commutation process are predicted, enhancing the performance analysis and optimization ability of the high-voltage hybrid DC circuit breaker, thereby being able to solve the reliability challenges faced by the load-commutated switch during the turn-off stage, and providing a solid theoretical basis and technical support for the design optimization and practical application of the high-voltage hybrid DC circuit breaker.

Description

Technical Field

[0001] The present invention relates to the technical field of DC circuit breakers, and particularly to a high-voltage hybrid DC circuit breaker. Background Art

[0002] In recent years, high-voltage direct current (HVDC) transmission systems have received extensive attention and development globally due to their unique advantages, such as the ability for point-to-point long-distance DC power transmission, the characteristic of maintaining the voltage polarity unchanged during power flow reversal, and the efficient interconnection ability with renewable energy and existing energy systems. However, despite its broad application prospects, the short-circuit fault protection problem of high-voltage DC transmission systems remains the main obstacle to its popularization.

[0003] To address this technical challenge, ABB, a leading company in the global power and automation technology field, with its profound R & D strength and industry experience, has proposed an innovative high-voltage hybrid DC circuit breaker. This circuit breaker is composed of a normal branch and a main circuit breaker branch connected in parallel. The normal branch contains an ultra-fast circuit breaker (UFD) and a load-commutated switch (LCS) connected in series, and the main circuit breaker branch is composed of multiple identical modules connected in series. Each module consists of a metal oxide arrester (MOA) and an IGBT connected in parallel to provide a strong fault current interruption ability.

[0004] In a high-voltage environment of hundreds of kilovolts, this high-voltage hybrid DC circuit breaker can quickly disconnect a fault current of thousands of amperes within an extremely short time (millisecond level), effectively ensuring the safety and stability of the power system. This technological breakthrough not only greatly improves the ability of high-voltage DC transmission systems to handle faults but also further enhances the reliability and resilience of the power grid, laying a solid foundation for the wide application and sustainable development of high-voltage DC transmission technology in the future.

[0005] However, with the continuous development of high-voltage hybrid DC circuit breaker technology, the complexity of its internal structure has become increasingly prominent. Especially the load-commutated switch (LCS) in the normal branch, due to its integration of IGBT switching elements, time-varying elements, and non-linear elements, exhibits strong non-linear time-varying characteristics, making it extremely complex to comprehensively understand the IGBT current-limiting mechanism of the main circuit breaker branch and predict the electrical characteristics of the load-commutated switch (LCS), which has become a key factor restricting the stability and performance improvement of the entire system.

[0006] Therefore, how to provide a modeling method for the load-commutated switch of a high-voltage hybrid DC circuit breaker to predict the dynamic response characteristics of the high-voltage hybrid DC circuit breaker during the commutation of the load-commutated switch has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0007] The object of the present invention is to provide a modeling method and application of a load commutated switch of a high-voltage hybrid DC circuit breaker, so as to overcome the deficiencies in predicting the dynamic response characteristics during the commutation of the load commutated switch (LCS) of the high-voltage hybrid DC circuit breaker in the prior art.

[0008] The present invention solves the above technical problems through the following technical solutions:

[0009] A modeling method of a load commutated switch of a high-voltage hybrid DC circuit breaker includes the following steps:

[0010] Step 1: Based on the simulation model of the high-voltage hybrid DC circuit breaker and the stray inductance L p , construct a simplified principle model of the high-voltage hybrid DC circuit breaker;

[0011] Step 2: Based on the simplified principle model, draw the fault current time sequence diagram and the fault voltage time sequence diagram of the high-voltage hybrid DC circuit breaker; based on the fault current time sequence diagram and the fault voltage time sequence diagram, determine the working characteristics that the power electronic switch needs to have in the high-voltage DC grid branch of the high-voltage hybrid DC circuit breaker;

[0012] Step 3: Based on the working characteristics that the power electronic switch needs to have, select the power electronic switch SPT-IGBT with such working characteristics, conduct a turn-off test on the SPT-IGBT, and establish a turn-off analysis model of the SPT-IGBT under the conditions of the extreme safe operating area;

[0013] Step 4: Optimize the load commutated switch IGBT-T LCS of the high-voltage hybrid DC circuit breaker, and combine the simplified principle model and the turn-off analysis model of the SPT-IGBT to establish an optimized turn-off equivalent circuit of the load commutated switch IGBT-T LCS ;

[0014] Step 5: Based on the optimized turn-off equivalent circuit and the turn-off analysis model of the load commutated switch IGBT-T LCS , build an optimized simulation model of the high-voltage hybrid DC circuit breaker.

[0015] A further improvement of the present invention is that in Step 1, the simplified principle model of the high-voltage hybrid DC circuit breaker includes a high-voltage DC grid branch, a normal state branch, and a main circuit breaker branch. The high-voltage DC grid branch is connected in series with the normal state branch. The normal state branch is a series connection of an ultra-fast circuit breaker UFD and a load commutated switch IGBT-T LCS , the main circuit breaker branch is connected in parallel with the normal state branch, and the series node of the high-voltage DC grid branch and the normal state branch is connected to the main circuit breaker branch through the stray inductance L p . The main circuit breaker includes a parallel connection of a lightning arrester MOA and an insulated gate bipolar transistor IGBT-T m .

[0016] A further improvement of the present invention lies in that: Step 2 specifically includes the following steps:

[0017] Based on the simplified principle model, simulate the commutation process of the load current, and draw the fault current time sequence diagram and fault voltage time sequence diagram of the high-voltage hybrid DC circuit breaker;

[0018] Based on the fault current time sequence diagram and fault voltage time sequence diagram, analyze the current limiting mechanism of the insulated gate bipolar transistor IGBT-T m and the dynamic switching process of the load commutation switch IGBT-T LCS to determine the operating characteristics that the load commutation switch IGBT-T LCS in the high-voltage DC power grid branch needs to possess.

[0019] A further improvement of the present invention lies in that: Step 3 specifically includes the following steps:

[0020] Based on the operating characteristics that the power electronic switch in the high-voltage DC power grid branch needs to possess, select the power electronic switch SPT-IGBT with such operating characteristics. Under the conditions of the extreme safe operating area, conduct a turn-off test on the SPT-IGBT, draw the turn-off time sequence diagram of the SPT-IGBT, analyze the turn-off process of the SPT-IGBT, and establish the turn-off equivalent circuit of the SPT-IGBT according to the turn-off process; Based on the turn-off equivalent circuit of the SPT-IGBT, conduct parameter calculation and establish the turn-off analytical model of the SPT-IGBT.

[0021] A further improvement of the present invention lies in that: Step 4 specifically includes the following steps:

[0022] Optimize the load commutation switch IGBT-T LCS of the high-voltage hybrid DC circuit breaker. Combine the simplified principle model and the turn-off analytical model of the SPT-IGBT to establish the turn-off analytical model of the optimized load commutation switch IGBT-T LCS Draw the turn-off time sequence diagram according to the turn-off analytical model, analyze the turn-off process of the optimized load commutation switch IGBT-T LCS and establish the turn-off equivalent circuit of the optimized load commutation switch IGBT-T LCS according to the turn-off process.

[0023] A further improvement of the present invention lies in that: The optimization specifically is: Connect a buffer circuit in parallel at the output port of the load commutation switch IGBT-T LCS .

[0024] A further improvement of the present invention lies in that: The buffer circuit adopts an RCD buffer circuit.

[0025] The present invention is further improved in that: Step 5 specifically includes the following steps: Based on the optimized load commutation switch IGBT-T LCS The shutdown equivalent circuit and shutdown analytical model are determined, the electrical parameters are determined, the simulation equivalent circuit is constructed, and based on the simulation equivalent circuit, an optimized simulation model of the high-voltage hybrid DC circuit breaker is built.

[0026] A further improvement of the present invention is that in step five, the electrical parameters include electrical parameters of the high voltage DC power grid branch, the normal branch and the main circuit breaker branch.

[0027] The present invention also provides an application of a high-voltage hybrid DC circuit breaker load flow switch simulation model, using an optimized simulation model built using the above-mentioned modeling method to predict the dynamic response characteristics of the high-voltage hybrid DC circuit breaker during load flow switch commutation.

[0028] Compared with the prior art, the positive and progressive effects of the present invention are:

[0029] The modeling method of the load commutation switch of the high-voltage hybrid DC circuit breaker provided by the present invention establishes a complete load commutation switch shutdown equivalent circuit by constructing a simplified principle model of the high-voltage hybrid DC circuit breaker and combining it with an accurate soft-through power electronic switch shutdown analytical model with the working characteristics of the high-voltage DC power grid under extreme safety working conditions; by setting the action timing diagram, the IGBT current limiting mechanism of the main circuit breaker branch in the high-voltage hybrid DC circuit breaker is revealed, and its dynamic characteristics in the load commutation process are predicted, thereby enhancing the performance analysis and optimization capabilities of the high-voltage hybrid DC circuit breaker, thereby being able to solve the reliability challenges faced by the load commutation switch in the shutdown stage, and providing a solid theoretical basis and technical support for the design optimization and practical application of the high-voltage hybrid DC circuit breaker.

[0030] Furthermore, the use of an RCD snubber circuit as a snubber circuit can achieve shock wave suppression, noise reduction and signal smoothing, voltage spike reduction, device protection, and high-frequency oscillation suppression. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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.

[0032] Figure 1 is a schematic diagram of a simulation model of a high voltage hybrid DC circuit breaker;

[0033] Figure 2 It is a simplified schematic diagram of the principle model;

[0034] Figure 3 It is a schematic diagram of the fault current and voltage timing;

[0035] Figure 4 It is a schematic diagram of the turn-off timing of SPT-IGBT under extreme SOA conditions;

[0036] Figure 5 It is the equivalent circuit and its graphical symbol of SPT-IGBT. Among them, Figure 5 (a)is a schematic diagram of the turn-off equivalent circuit of SPT-IGBT, Figure 5 (b)is Figure 5 the graphical symbol of (a);

[0037] Figure 6 It is a schematic diagram of the turn-off equivalent circuit of the optimized load-commutated switch IGBT-T LCS ;

[0038] Figure 7 It is a schematic diagram of the turn-off timing of the optimized load-commutated switch IGBT-T LCS ;

[0039] Figure 8 It is a schematic diagram of the turn-off equivalent circuit of the optimized load-commutated switch IGBT-T LCS in the interval [t 0 , t 1 ;

[0040] Figure 9 It is a schematic diagram of the turn-off equivalent circuit of the optimized load-commutated switch IGBT-T LCS in the interval [t 1 , t 2 ;

[0041] Figure 10 It is a schematic diagram of the turn-off equivalent circuit of the optimized load-commutated switch IGBT-T LCS in the interval [t 2 , t 3 ;

[0042] Figure 11 It is a schematic diagram of the simulation equivalent circuit;

[0043] Figure 12 It is a schematic diagram of the simulation and experimental voltage curves of the unoptimized simulation model. Among them, ① is the experimental voltage curve and ② is the simulation voltage curve;

[0044] Figure 13 It is a schematic diagram of the simulation and experimental current curves of the unoptimized simulation model. Among them, ③ is the experimental current curve and ④ is the simulation current curve;

[0045] Figure 14 It is a schematic diagram of the simulation and experimental voltage curves of the optimized simulation model. Among them, ① is the experimental voltage curve and ② is the simulation voltage curve;

[0046] Figure 15 It is a schematic diagram of the simulation and experimental current curves for optimizing the simulation model. Among them, ③ is the experimental current curve, and ④ is the simulation current curve. Specific implementation manners

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0048] In the description of the present invention, it should be understood that the terms "include" and "comprise" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0049] It should also be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms.

[0050] It should be further understood that the term " / and" used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in the present invention generally represents an "or" relationship between the contextually related objects.

[0051] It should be understood that although the terms first, second, third, etc. may be used in the embodiments of the present invention to describe preset ranges, etc., these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from each other. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0052] Depending on the context, as used herein, the word "if" can be interpreted as "when" or "while" or "in response to determining" or "in response to detecting". Similarly, depending on the context, the phrase "if determined" or "if detecting (stated condition or event)" can be interpreted as "when determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)".

[0053] Schematic diagrams of various structures according to the disclosed embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, where for the purpose of clear illustration, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary, and in practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0054] The following further elaborates on the present invention in conjunction with the accompanying drawings and specific embodiments, which is an explanation rather than a limitation of the present invention.

[0055] A modeling method for a load commutation switch of a high-voltage hybrid DC circuit breaker includes the following steps:

[0056] Step 1: Based on the simulation model of the high-voltage hybrid DC circuit breaker and the stray inductance L p , construct a simplified principle model of the high-voltage hybrid DC circuit breaker;

[0057] Step 2: Based on the simplified principle model, draw the fault current time sequence diagram and the fault voltage time sequence diagram of the high-voltage hybrid DC circuit breaker; based on the fault current time sequence diagram and the fault voltage time sequence diagram, determine the operating characteristics that the power electronic switch needs to possess in the high-voltage DC grid branch of the high-voltage hybrid DC circuit breaker;

[0058] Step 3: Based on the operating characteristics that the power electronic switch needs to possess, select the power electronic switch SPT-IGBT with such operating characteristics, conduct a turn-off test on the SPT-IGBT, and establish a turn-off analysis model of the SPT-IGBT under extreme safe operating area conditions;

[0059] Step 4: Optimize the load commutation switch IGBT-T of the high-voltage hybrid DC circuit breaker LCS , and combine the simplified principle model and the turn-off analysis model of the SPT-IGBT to establish an equivalent turn-off circuit of the optimized load commutation switch IGBT-T LCS ;

[0060] Step 5: Based on the optimized load commutation switch IGBT-T LCSThe turn-off equivalent circuit and turn-off analysis model are used to determine electrical parameters, and an optimized simulation model of the high-voltage hybrid DC circuit breaker is built based on the electrical parameters.

[0061] The modeling method of the load-commutated switch of the high-voltage hybrid DC circuit breaker provided by the present invention builds a complete turn-off equivalent circuit of the load-commutated switch by constructing a simplified principle model of the high-voltage hybrid DC circuit breaker and combining an accurate soft turn-on power electronic switch turn-off analysis model with the working characteristics of the high-voltage DC power grid under extreme safe operating area conditions; by setting the action timing diagram, it reveals the IGBT current-limiting mechanism of the main circuit breaker branch in the high-voltage hybrid DC circuit breaker and predicts its dynamic characteristics during the load commutation process, enhancing the performance analysis and optimization ability of the high-voltage hybrid DC circuit breaker, thereby being able to solve the reliability challenges faced by the load-commutated switch during the turn-off stage and providing a solid theoretical basis and technical support for the design optimization and practical application of the high-voltage hybrid DC circuit breaker.

[0062] Specifically, in step one, the simplified principle model of the high-voltage hybrid DC circuit breaker includes a high-voltage DC power grid branch, a normal state branch, and a main circuit breaker branch. The high-voltage DC power grid branch is in series with the normal state branch. The normal state branch is a series connection of an ultra-fast circuit breaker UFD and a load-commutated switch IGBT-T LCS , the main circuit breaker branch is in parallel with the normal state branch, and the series node of the high-voltage DC power grid branch and the normal state branch is connected to the main circuit breaker branch through a stray inductance L p , and the main circuit breaker includes a parallel connection of a lightning arrester MOA and an insulated gate bipolar transistor IGBT-T m .

[0063] Specifically, step two specifically includes the following steps:

[0064] Based on the simplified principle model, simulate the commutation process of the load current, and draw the fault current timing diagram and fault voltage timing diagram of the high-voltage hybrid DC circuit breaker;

[0065] Based on the fault current timing diagram and fault voltage timing diagram, analyze the current-limiting mechanism of the insulated gate bipolar transistor IGBT-T m and the dynamic switching process of the load-commutated switch IGBT-T LCS , and determine the working characteristics that the load-commutated switch IGBT-T LCS in the high-voltage DC power grid branch needs to possess.

[0066] Specifically, step three specifically includes the following steps:

[0067] Based on the operating characteristics required by the power electronic switch in the branch of the high-voltage DC power grid, the power electronic switch SPT-IGBT with such operating characteristics is selected. Under the conditions of the extreme safe operating area, the turn-off test of the SPT-IGBT is carried out, the turn-off timing diagram of the power electronic switch SPT-IGBT is drawn, the turn-off process of the power electronic switch SPT-IGBT is analyzed, and based on the turn-off process, the turn-off equivalent circuit of the power electronic switch SPT-IGBT is established; based on the turn-off equivalent circuit of the power electronic switch SPT-IGBT, parameter calculation is carried out to establish the turn-off analytical model of the power electronic switch SPT-IGBT.

[0068] Specifically, step four specifically includes the following steps:

[0069] Optimize the load commutation switch IGBT-T of the high-voltage hybrid DC circuit breaker, LCS combine the simplified principle model and the turn-off analytical model of the power electronic switch SPT-IGBT to establish the optimized load commutation switch IGBT-T LCS turn-off analytical model, draw the turn-off timing diagram according to the turn-off analytical model, analyze the turn-off process of the optimized load commutation switch IGBT-T LCS and based on the turn-off process, establish the turn-off equivalent circuit of the optimized load commutation switch IGBT-T LCS

[0070] Specifically, the optimization is as follows: a buffer circuit is connected in parallel at the output port of the load commutation switch IGBT-T LCS

[0071] Specifically, the buffer circuit adopts an RCD buffer circuit; using an RCD buffer circuit as the buffer circuit can achieve shock wave suppression, noise reduction and signal smoothing, voltage spike reduction, device protection and high-frequency oscillation suppression.

[0072] Specifically, step five specifically includes the following steps: based on the turn-off equivalent circuit and the turn-off analytical model of the optimized load commutation switch IGBT-T LCS determine the electrical parameters, construct the simulation equivalent circuit, and based on the simulation equivalent circuit, build the optimized simulation model of the high-voltage hybrid DC circuit breaker.

[0073] Specifically, in step five, the electrical parameters include the electrical parameters of the high-voltage DC power grid branch, the normal branch and the main circuit breaker branch.

[0074] Based on the same inventive concept, the present invention also provides an application of the load flow switch simulation model of the high-voltage hybrid DC circuit breaker. The optimized simulation model built by using the above modeling method is used to predict the dynamic response characteristics of the high-voltage hybrid DC circuit breaker during the commutation of the load commutation switch. ​​

[0075] In a specific embodiment of the present invention, a modeling method for a load commutation switch of a high-voltage hybrid DC circuit breaker includes the following steps:

[0076] Step 1 specifically includes:

[0077] Step 1.1, ABB Company establishes a principle model of a high-voltage hybrid DC circuit breaker with IGBT as an electronic switch, which consists of three parts: the equivalent circuit branch of the high-voltage DC power grid, the normal branch, and the main circuit breaker;

[0078] See Figure 1 , part ① is the equivalent circuit branch of the high-voltage DC power grid, part ② is the normal branch, and part ③ is the main circuit breaker. IGBT-T m is used as an electronic switch to replace the thyristor; the equivalent circuit of the high-voltage DC power grid (part ①) is electrically connected to the normal branch (part ②) to provide a power transmission path; in the normal working state, the normal branch remains closed to allow current to pass through; the main circuit breaker (part ③) is connected in series with the normal branch and is connected to the equivalent circuit of the high-voltage DC power grid by controlling the switch state; in the fault-free state, the main circuit breaker remains closed to maintain the continuous operation of the circuit; when a fault or abnormal situation occurs, the main circuit breaker quickly disconnects, thereby cutting off the current flow to the normal branch and ensuring the safety of the power grid system.

[0079] Step 1.2, on the basis of Step 1.1, add the stray inductance L of the main circuit breaker between the normal branch and the main circuit breaker branch P , and construct a simplified principle model of the high-voltage hybrid DC circuit breaker. See Figure 2 .

[0080] Step 2 specifically includes:

[0081] Step 2.1, based on the simplified principle model of the high-voltage hybrid DC circuit breaker, draw the fault current time sequence diagram and fault voltage time sequence diagram of the high-voltage hybrid DC circuit breaker. See Figure 3 .

[0082] Step 2.2, based on the fault current time sequence diagram and fault voltage time sequence diagram of the high-voltage hybrid DC circuit breaker, study the current limiting mechanism of IGBT-T m (the power electronic switch of the main circuit breaker) and the dynamic switching process of the load commutation switch IGBT-T LCS . In the high-voltage DC power transmission system, 1.2 times the maximum rated current is set as the trigger threshold I LST for short-circuit fault protection. In the interval [0, t 0 , it is the normal working condition, and the load current i Ls flows through the normal branch to the load. In the interval [t 0 , t1 interval, a short-circuit fault occurs in the DC transmission line, and the fault current i Ls rapidly increases from the normal value I norm . [t 1 , t 2 interval, the current flowing through the stray inductance L p cannot jump, and the current through the IGBT-T m gradually increases. The fault current i Ls passes through the normal branch and the switch branch of the main circuit breaker at the same time. [t 2 , t 3 interval, the IGBT-T LCS (load commutation switch) is completely turned off, and the current i LCS through the normal branch drops to zero. The fault current is forced to commutate from the normal branch to the main circuit breaker branch. At the same time, the two contacts of the ultra-fast circuit breaker (UFD) begin to gradually separate until completely disconnected. [t 3 , t 4 interval, the fault voltage u Tm rises to the rated voltage U r of the metal oxide arrester (MOA). The MOA enters the pre-breakdown region, and the inductive current i p gradually commutates from the IGBT-T m to the energy absorption branch of the MOA. The fault current i Ls reaches the maximum value I max in a short time. [t 4 , t 5 interval, the MOA enters the breakdown region, and u Tm rises to the reference voltage U ref of the MOA. The reference voltage U ref is equal to 1.5 times the rated DC voltage U dc . Under the action of the MOA, the fault current i Ls linearly decreases until it becomes zero.

[0083] Step 2.3, according to the above analysis process, it is found that the high-voltage DC grid has a fault current i when a short-circuit fault occurs LsThe characteristics of rapid development are as follows: the transient current has a fast rising speed and the steady-state current peak value is high. Therefore, for the application of flexible DC transmission systems, the IGBTs used should have the important working characteristic of being able to provide a larger short-circuit safe operating area (SOA) to adapt to the harsh working environment faced by high-voltage DC grids under short-circuit conditions, ensuring that the IGBTs can work safely and reliably when short-circuit faults occur and avoiding damage or failure. This requires that the high-voltage hybrid DC circuit breaker can respond quickly to ensure that the switching devices in the equipment can be turned off and on in a timely manner. In addition, considering the advantages of high power and low loss of high-voltage DC systems, the IGBTs applied to such systems should have important working characteristics such as large capacity (including high maximum withstand voltage and rated current), high switching speed, and low loss to meet the strict requirements of high-voltage DC grids for reliability and efficiency.

[0084] Step 3 specifically includes:

[0085] Step 3.1: According to the working characteristic requirements of IGBTs for hybrid high-voltage circuit breakers in the high-voltage DC grid in Step 2, select a power electronic switch of the SPT-IGBT type. The SPT-IGBT is a soft punch-through power electronic switch, which is a new type of IGBT proposed by ABB for high-voltage and high-power applications, named SPT-IGBT; based on the physical structure of the SPT-IGBT, combined with semiconductor physics theory and circuit theory, conduct a turn-off test of the SPT-IGBT under extreme SOA conditions, draw the turn-off waveform, and study the turn-off process of the SPT-IGBT to establish the turn-off equivalent circuit of the SPT-IGBT.

[0086] Specifically: Conduct turn-off tests on multiple SPT-IGBTs with rated voltages of 3.3 kV to 6.5 kV under extreme SOA conditions, and draw the turn-off timing diagram. See Figure 4 , and through analysis, the following turn-off process can be obtained: when t < t o , the SPT-IGBT is in the deep saturation region, and the output current i c and the output voltage u ce remain unchanged; when t o ≤ t < t 1 , the Miller capacitor C gc is charged approximately at a constant current, causing the output voltage u ce to increase; when t 1 ≤ t < t 2 , when u ce = U DA , dynamic avalanche starts, and begins to consume the electron-hole pairs stored inside the device; when t 2 ≤ t < t 3 , u ce is greater than the power supply voltage U DC , the inductor Ls The voltage at both ends reverses, and the current begins to decline; t 3 ≤t < t 4 When, the electron-hole pairs stored inside the device are all consumed, and the collector current of the SPT-IGBT drops to zero, entering the self-clamping mode; when t > t 4 When, the SPT-IGBT is completely turned off; the external circuit begins to enter the resonance stage of the RLC series circuit; therefore, the SPT-IGBT contains five operating states, including turn-on, turn-off, constant current, dynamic avalanche, and switching self-clamping mode;

[0087] Based on the electrical symbol of the standard IGBT, establish the turn-off equivalent circuit of the SPT-IGBT according to the turn-off process, see Figure 5 This equivalent circuit is composed of an n-channel MOSFET T 3 driving a PNP bipolar junction transistor T 1 emitter follower transistor, and T 2 is an NPN transistor. R m is the conductivity modulation resistance of the n-base region of the SPT-IGBT, and the diode D p and the virtual capacitor C p connected in parallel with it connect the base and the collector to describe the dynamic avalanche phenomenon and its electrical characteristics of the SPT-IGBT. The Zener diode D ZRm charges the virtual capacitor C p constantly to describe the linear smooth growth of the output voltage u ce of the device during dynamic avalanche. The Zener diode D z connects the collector and the emitter to simulate the switching self-clamping mode.

[0088] Step 3.2, perform parameter calculation for the turn-off equivalent circuit of the SPT-IGBT, including the conductivity modulation resistance R m , the p+ base region bulk resistance R s , the virtual capacitor C p , and determine the accurate turn-off analytical model of the SPT-IGBT, specifically including: calculating the conductivity modulation resistance R m , indirectly calculating the saturation voltage of the SPT-IGBT by calculating the total voltage of the series branch composed of the three components T 1 , R m and T 3 ; according to KVL, the expression of the IGBT saturation voltage obtained by superimposing the three parts of the voltage is:

[0089]

[0090] In the formula, U T is the thermoelectric potential (25 mV at room temperature); I Cis the collector current of the SPT-IGBT; I s is the reverse saturation current of the base-emitter junction; α NPN is the current gain of the NPN transistor T 1 ; R m is the modulation resistance of the n-base region; R T3（on） is the on-resistance of the MOSFET T 3 ;

[0091] From Figure 4 it can be obtained that when t < t o , the IGBT has entered the deep saturation state, and the output voltage u ce is equal to the collector-emitter saturation voltage U ce (sat) . Therefore, the calculation formula of the conductance modulation resistance R m(sat) is,

[0092]

[0093] In the formula, U ce (sat) is the collector-emitter saturation voltage, U T3（on） is the on-voltage of the MOSFET T3, I C is the collector current of the SPT-IGBT, α NPN is the current gain of the NPN transistor T 1 ;

[0094] Step 3.3.2, calculate the p + base region bulk resistance R s , during the conduction of T 3 , the capacitor C p and R s are connected in parallel and have the same voltage, expressed as,

[0095]

[0096] In the formula, u Cp is the voltage across the capacitor C p , u Rs is the voltage across the p + base region bulk resistance R s , i T1 is the current of the transistor T 1 , α NPN is the current gain of the NPN transistor T 1 , I C is the collector current of the SPT-IGBT;

[0097] To suppress the current latch-up phenomenon of the SPT-IGBT, even if the current I c reaches its maximum value I cmax , it is also required that the voltage uRs Less than 0.5V to avoid T 2 Turn-on and the occurrence of its current holding phenomenon, expressed as

[0098]

[0099] In the formula, I cmax Is the maximum value of the current I c Of, I cnom Is the rated value of the collector DC current;

[0100] The p+-base region bulk resistance R s The expression is calculated as

[0101]

[0102] Calculate the virtual capacitance C p , from Figure 4 The rising slope of u can be obtained as ce Of

[0103]

[0104] In the formula, u ce Is the collector-emitter voltage, Uz is the Zener breakdown threshold voltage, U DA Is u ce Rises to the threshold voltage of dynamic avalanche, I o Is the output current, C p Is the virtual capacitance;

[0105] From the above formula, the formula for calculating C p Is

[0106]

[0107] Step 4 specifically includes:

[0108] Step 4.1, add a conventional RCD buffer circuit to the load commutation switch IGBT-T of the high-voltage hybrid DC circuit breaker for optimization to reduce dv / dt and reduce turn-off losses; then, according to the simplified principle model of the high-voltage hybrid DC circuit breaker in Step 2 and the accurate SPT-IGBT turn-off analysis model in Step 3, establish an optimized load commutation switch IGBT-T LCS Turn-off analysis model, see LCS ; Figure 6 ;

[0109] Study the turn-off analysis model, which consists of four parts. Part ① uses a DC voltage source U dc To represent the high-voltage DC power supply device; Part ② is the stray inductance L p And the ideal switch S TmThe series circuit formed; ③ The part is the normal branch, where the model of the UFD is an ideal current-controlled switch with a 2ms delay, serving as the load-commutated switch IGBT-T LCS It is not a standard IGBT but an SPT-IGBT; Part ④ is a conventional RCD snubber circuit, connected in parallel to the output port of IGBT-T LCS .

[0110] Step 4.2, according to the turn-off analysis model, set the turn-off timing diagram of the conventional RCD snubber circuit, see Figure 7 ; Through analysis, it can be obtained that the turn-off process is as follows: when t ≤ t 0 , the current of IGBT-T LCS is equal to I LST , and the output voltage U ce is approximately zero. When t 0 < t ≤ t 1 , it is the turn-off process of the LCS. The voltage waveform of IGBT-T LCS depends on the charging waveform of the snubber capacitor C s .

[0111] According to the analysis of the turn-off timing diagram, the current expression during the turn-off process of IGBT-T LCS is:

[0112]

[0113] Where, t f is the turn-off time of IGBT-T LCS , I LST is the current passing through the current-limiting reactor L s , i c1 is the load current. For the sake of simplified analysis, it is assumed that I LST remains constant.

[0114] According to the above analysis, establish the turn-off equivalent circuit of the load-commutated switch IGBT-T LCS at each timing, specifically: during the charging interval [t s , t 0 , t 1 of the snubber capacitor C LCS , IGBT-T m turns off, IGBT-T Tm turns on simultaneously, and the ideal switch S d is in the closed state. The equivalent circuit is an undamped parallel resonant circuit driven by a ramp current source i Figure 8 ; during the switch self-clamping mode interval [t 1 , t 2 of IGBT-T LCSEnter the self-clamping mode range of the switch, u Cs is approximately equal to U SSCM , for the turn-off equivalent circuit in this stage, see Figure 9 , the circuit model of the Zener diode D z is a DC voltage source with an amplitude of U SSCM ; during the discharge interval [t 2 , t 3 of the buffer capacitor Cs, IGBT-T LCS is completely turned off, the Zener diode D z stops clamping, and the buffer capacitor C s starts to discharge through R s , UFD and L p , for the turn-off equivalent circuit in this stage, see Figure 10 .

[0115] Step 5 specifically includes:

[0116] Step 5.1, based on the turn-off equivalent circuit and turn-off analysis model of the optimized load commutation switch IGBT-T LCS , determine the electrical parameters of the HVDC grid branch, normal branch, and main circuit breaker branch, and construct the PSCAD / EMTDC simulation equivalent circuit of the hybrid HVDC circuit breaker. Specifically: for the normal branch ②, in the simulation circuit, model UFD with an ideal switch with a delay time of 0.25 - 2 ms; the device used for IGBT-T LCS is an SPT-IGBT module with a breakdown voltage of 3.3 kV or 4.5 kV; for the main circuit breaker ③, it is composed of 4 80 kV modules in series; the RCD buffer circuit is a conventional RCD buffer circuit; R L is the load of the DC system under normal operating conditions.

[0117] Step 5.2, based on the PSCAD / EMTDC simulation equivalent circuit of the hybrid HVDC circuit breaker, build an optimized simulation model of the hybrid HVDC circuit breaker, see Figure 11 , determine the experimental parameters related to L s , C s and U dc to predict the dynamic response characteristics of the hybrid HVDC circuit breaker during the commutation of the load commutation switch. Specifically: the power supply voltage U dc = 40 kV, the output current I o = 3.07 kA, the inductance L s = 25 mH, the stray inductance L p = 24 μH, the buffer capacitor C s = 13 μF, the output capacitance C LCS of IGBT-T ou1 = 250 nF, the junction capacitance C of the reverse blocking diodeD2 = 49 nF, using an 80 kV IGBT-T m module as the switching branch of the main circuit breaker;

[0118] Analyze the simulation results and experimental waveforms of the simulation model of the unoptimized high-voltage hybrid DC circuit breaker. See Figure 12 and Figure 13 , where the solid lines ① and ③ represent the voltage and current curves of the experimental waveforms respectively, and the dashed lines ② and ④ represent the voltage and current curves of the simulation results. It can be seen from the figure that the changing trends of the simulation curves and the experimental curves are consistent, and the current curve is better than the voltage simulation curve. This indicates that the system model can qualitatively characterize the overall characteristics of the load commutation switch IGBT-T LCS commutation process. However, at special points such as A, B, C, D, E, and F, there are significant errors between the simulation results and the experimental results, which cannot meet the engineering requirements. One of the reasons for the errors is that a new type of SPT-IGB is adopted in the hybrid circuit breaker; there is only a standard IGBT model in the PSCAD / EMTD component library, and there is no SPT-IGBT model of any type. Therefore, the system model has certain reference value for the qualitative analysis of the hybrid circuit breaker, but cannot complete the quantitative analysis.

[0119] Analyze the simulation results and experimental waveforms of the optimized simulation model of the high-voltage hybrid DC circuit breaker. See Figure 14 and Figure 15 , where the solid lines ① and ③ represent the voltage and current curves of the experimental waveforms respectively, and the dashed lines ② and ④ represent the voltage and current curves of the simulation results. It can be seen from the figure that the simulation curves and the experimental curves coincide highly, and the analysis errors are all within 5%.

[0120] In summary, it can be seen that the optimized simulation model constructed by using the modeling method of the present invention has more excellent performance than the traditional system model, can accurately predict the dynamic response characteristics of the high-voltage hybrid DC circuit breaker during the commutation process of the load commutation switch, and solves the reliability problem existing in the turn-off process of the load commutation switch of the high-voltage hybrid DC circuit breaker in the prior art; it provides an effective analysis tool for the research of the buffer circuit of the load commutation switch branch and the design of the main circuit breaker MOA module. This modeling method provides a theoretical basis and technical support for the optimized design and practical application of the high-voltage hybrid DC circuit breaker.

[0121] The above content is only to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A modeling method for a load commutation switch of a high-voltage hybrid DC circuit breaker, characterized in that: The following steps are involved: Step 1: Based on the simulation model of high-voltage hybrid DC circuit breaker and stray inductance L p , construct a simplified principle model of high-voltage hybrid DC circuit breaker; Step 2: Based on the simplified principle model, draw the fault current timing diagram and the fault voltage timing diagram of the high-voltage hybrid DC circuit breaker; based on the fault current timing diagram and the fault voltage timing diagram, determine the working characteristics that the power electronic switch needs to have in the high-voltage DC power grid branch of the high-voltage hybrid DC circuit breaker; Step 3: Based on the working characteristics that the power electronic switch needs to have, select a power electronic switch SPT-IGBT with the working characteristics, perform a shutdown test on the SPT-IGBT, and establish a shutdown analytical model of the SPT-IGBT under extreme safety working area conditions; Step 4: Load commutation switch IGBT-T of high voltage hybrid DC circuit breaker LCS Optimize and combine the simplified principle model and the SPT-IGBT turn-off analytical model to establish the optimized load commutation switch IGBT-T LCS The turn-off equivalent circuit of Step 5: Based on the optimized load commutation switch IGBT-T LCS The shutdown equivalent circuit and shutdown analytical model are used to build an optimized simulation model of high-voltage hybrid DC circuit breaker; In step 1, the simplified principle model of the high-voltage hybrid DC circuit breaker includes a high-voltage DC grid branch, a normal branch and a main circuit breaker branch. The high-voltage DC grid branch is connected in series with the normal branch. The normal branch is an ultra-fast circuit breaker UFD and a load commutation switch IGBT-T connected in series. LCS , the main circuit breaker branch is connected in parallel with the normal branch, and the series node of the high-voltage DC grid branch and the normal branch is connected through the stray inductance L p Connect the main circuit breaker branch, the main circuit breaker includes a parallel lightning arrester MOA and an insulated gate bipolar transistor IGBT-T m .

2. A modeling method for a high-voltage hybrid DC circuit breaker load commutation switch according to claim 1, characterized in that: Step 2 specifically includes the following steps: Based on the simplified principle model, the commutation process of the load current is simulated, and the fault current timing diagram and fault voltage timing diagram of the high-voltage hybrid DC circuit breaker are drawn; Based on the fault current timing diagram and fault voltage timing diagram, analyze the insulated gate bipolar transistor IGBT-T m Current limiting mechanism and load commutation switch IGBT-T LCS The dynamic switching process of the load commutation switch IGBT-T in the high-voltage DC grid branch is determined LCS Required job characteristics.

3. A modeling method for a load commutation switch of a high-voltage hybrid DC circuit breaker according to claim 2, characterized in that: Step three specifically includes the following steps: Based on the working characteristics that the power electronic switch in the high-voltage DC power grid branch needs to have, a power electronic switch SPT-IGBT with such working characteristics is selected, and a shutdown test is performed on the SPT-IGBT under the conditions of the extreme safe working area. The shutdown timing diagram of the SPT-IGBT is drawn, and the shutdown process of the SPT-IGBT is analyzed. According to the shutdown process, the shutdown equivalent circuit of the SPT-IGBT is established; based on the shutdown equivalent circuit of the SPT-IGBT, parameter calculation is performed and a shutdown analytical model of the SPT-IGBT is established.

4. A modeling method for a high-voltage hybrid DC circuit breaker load commutation switch according to claim 3, characterized in that: Step 4 specifically includes the following steps: Load commutation switch IGBT-T for high voltage hybrid DC circuit breaker LCS Optimize and combine the simplified principle model and the SPT-IGBT turn-off analytical model to establish the optimized load commutation switch IGBT-T LCS Turn-off analytical model, based on the turn-off analytical model, draw the turn-off timing diagram and analyze the optimized load commutation switch IGBT-T LCS According to the shutdown process, an optimized load commutation switch IGBT-T is established. LCS The turn-off equivalent circuit.

5. A modeling method for a load commutation switch of a high-voltage hybrid DC circuit breaker according to claim 4, characterized in that: The optimization is specifically as follows: in the load commutation switch IGBT-T LCS The output port is connected in parallel with the buffer circuit.

6. A modeling method for a high-voltage hybrid DC circuit breaker load commutation switch according to claim 5, characterized in that: The buffer circuit adopts an RCD buffer circuit.

7. A modeling method for a load commutation switch of a high-voltage hybrid DC circuit breaker according to claim 4, characterized in that: Step 5 specifically includes the following steps: Based on the optimized load commutation switch IGBT-T LCS The shutdown equivalent circuit and shutdown analytical model are determined, the electrical parameters are determined, the simulation equivalent circuit is constructed, and based on the simulation equivalent circuit, an optimized simulation model of the high-voltage hybrid DC circuit breaker is built.

8. A modeling method for a high-voltage hybrid DC circuit breaker load commutation switch according to claim 7, characterized in that: In step 5, the electrical parameters include electrical parameters of the high voltage DC grid branch, the normal branch and the main circuit breaker branch.

9. An application of a high voltage hybrid DC circuit breaker load current switch simulation model, characterized in that: The optimization simulation model constructed by the modeling method as described in any one of claims 1 to 8 above is used to predict the dynamic response characteristics of the high-voltage hybrid DC circuit breaker during the commutation period of the load commutation switch.

Images