Thyristor physical equivalent simulation method considering transient characteristics of nonlinear switch

Abstract

The invention relates to a thyristor physical equivalent simulation method considering transient characteristics of a nonlinear switch, and belongs to the field of equivalent modeling considering turn-off characteristics of a thyristor device in the field of high-voltage direct-current power transmission. The method comprises the following steps: correcting the difference between the turn-off characteristics of thyristors with different voltage levels, and establishing a thyristor physical model for realizing the consistency of the transient characteristics of nonlinear switches of the thyristors with different voltage levels; according to a physical equivalence method of connecting compensation branches at two ends of a low-voltage small-current thyristor in parallel, reverse recovery current of the low-voltage thyristor is compensated through discharge of a capacitor in a resistance-capacitance branch, and loop current is transferred to a turn-off time compensation branch through switching of a bidirectional switch after the low-voltage thyristor is turned off. And dynamic consistency of nonlinear switching characteristics of the model thyristor and the prototype thyristor is realized. Meanwhile, a parameter selection method and a switch switching method of each component in the physical equivalent model are provided, so that the equivalent accuracy of the model thyristor to the turn-off characteristic of the prototype thyristor is ensured.

Description

Technical Field

[0001] The present invention relates to the field of high-voltage direct current transmission, and in particular to the field of equivalent modeling of the turn-off characteristics of thyristor devices, and in particular to a physical equivalent simulation method of thyristors that takes into account the transient characteristics of nonlinear switches. By analyzing the differences in the turn-off characteristics of thyristors of different voltage levels, a physical equivalent method that takes into account the switching characteristics of thyristors and a correction method for deviations generated in the physical equivalent process are proposed, and a physical equivalent model of thyristors that takes into account the consistency of the transient characteristics of nonlinear switches is constructed, which is of great significance for the study of commutation failures in high-voltage direct current transmission systems. Background Art

[0002] High Voltage Direct Current (HVDC) has the advantages of rapid system adjustment, huge transmission capacity, and strong long-distance transmission capability. Line Commutated Converter (LCC) has been widely used in existing HVDC transmission projects due to its large transmission capacity and good economy. Its operating characteristics have a huge impact on the entire HVDC transmission system.

[0003] However, due to the turn-off characteristics of the thyristor itself, it cannot be completely turned off at the instant of the reverse voltage, resulting in commutation failure in the system, which causes great harm to the LCC-HVDC system. Therefore, it is urgent to conduct in-depth research on the occurrence mechanism, influencing factors, and defense methods of commutation failure. At present, the research on commutation failure is mainly carried out through simulation technology. Compared with digital simulation, physical simulation technology can more accurately reproduce the operating conditions and various physical processes of the actual system, and can better reflect the nonlinear transient characteristics of each component in the actual system. It is more suitable for the study of the influence of internal and external factors on commutation failure in high-voltage direct current transmission systems and commutation failure defense methods. In the existing research on thyristor physical equivalent methods, most of them adopt the method of proportionally reducing various parameters according to the proportional relationship between the required voltage level and the actual voltage level, or using similar principles to approximate the thyristor reverse recovery characteristics to select the model thyristor model, but these existing physical equivalent methods will lead to differences in physical characteristics between the physical model and the prototype, resulting in deviations in the dynamic physical processes of the two. Especially for the physical equivalence of thyristors, the core components of converters, the accuracy of its simulation determines whether the physical model can reflect the actual operating conditions of the actual system. However, the existing equivalent methods often ignore the transient characteristics of thyristors and only use low-voltage thyristors as substitutes. Therefore, it is difficult to ensure the authenticity and validity of subsequent research results. Summary of the invention

[0004] The purpose of the present invention is to provide a thyristor physical equivalent simulation method that takes into account the transient characteristics of nonlinear switches, which solves the problem of ignoring the reverse recovery process of thyristors and the deviation that will occur in the physical equivalent process in the prior art, and greatly improves the accuracy of thyristor physical simulation. The present invention analyzes the characteristics of carrier changes during the shutdown process of the thyristor, the core device of the converter, and then studies the shutdown mechanism of the thyristor. The differences between the shutdown characteristics of thyristors of different voltage levels are analyzed, a method for correcting the differences is proposed, and a thyristor physical equivalent model that considers the consistency of nonlinear switching transient characteristics is constructed. A method for selecting parameters of each component in the physical equivalent model is proposed, and a switch switching method is proposed based on the differences in the shutdown characteristics of thyristors of different voltage levels, so as to achieve dynamic consistency of the shutdown characteristics of thyristors of different voltage levels. The model can be used for the study of the mechanism of commutation failure, influencing factors, and defense methods.

[0005] The thyristor turn-off process can be divided into two parts: the reverse recovery process and the forward blocking recovery process. During this period, the carrier concentration changes continuously. Only when the carrier concentration is close to 0, the thyristor is completely turned off and the forward blocking effect is restored. Thyristors of different voltage levels have different internal carrier concentrations and different carrier dissipation rates, which leads to certain differences in the turn-off characteristics of the two. In view of this difference, the present invention proposes a thyristor physical equivalent method that connects a compensation branch in parallel at both ends of a low-voltage and low-current thyristor to compensate for the difference in the turn-off characteristics of the two, and establishes a thyristor physical equivalent model. At the same time, a method for selecting parameters of each component in the physical equivalent model and a switch switching method are proposed to ensure that the nonlinear switching characteristics of the model thyristor and the prototype thyristor are dynamically consistent.

[0006] The above-mentioned object of the present invention is achieved by the following technical solutions: The physical equivalent simulation method of thyristor considering the transient characteristics of nonlinear switch includes the following steps: Step 1: Correct the differences between the turn-off characteristics of thyristors of different voltage levels, and establish a thyristor physical model that achieves consistent nonlinear switching transient characteristics of thyristors of different voltage levels; Step 1.1: Compare the forward conduction current of thyristors with different voltage levels I F , reverse recovery current peak I RM And the off time t rr , analyze the differences between the turn-off characteristics of thyristors at different voltage levels; Step 1.2: Analyze system commutation time t r Thyristor turn-off time with low voltage level t L , high voltage thyristor turn-off timet H The influence of the relationship between the three on the commutation process; Step 1.3: Establish a physical model of the thyristor, use a parallel damping branch to compensate for the reverse recovery current of the thyristor, and switch the switch by judging the direction of the voltage across the thyristor; Step 2: Based on the operating principle of the thyristor physical equivalent model, a method for selecting the parameters of the resistor and capacitor in the RC branch of the thyristor physical model is proposed; Step 2.1: By comparing the reverse recovery current differences of thyristors with different voltages, the parameters of the capacitor C in the RC branch are determined to compensate for the reverse recovery current differences; Step 2.2: Determine the parameters of the resistor R in the branch according to the maximum current that the RC branch can withstand.

[0007] Step 3: According to the different stages of the high voltage thyristor turn-off process, a switch switching method is used to achieve the same turn-off characteristics of thyristors of different voltage levels, specifically: Step 3.1: When the high voltage thyristor enters the reverse recovery current increasing stage, the RC branch switch is turned on, and the capacitor discharge is used to compensate for the reverse recovery current difference; Step 3.2: When the reverse recovery current of the high voltage thyristor reaches a peak value, the RC branch cut-off switch is turned off; Step 3.3: After the low voltage thyristor is turned off, the off time compensation branch switch is turned on, so that the current is transferred to the branch, indirectly extending the off time of the low voltage thyristor; Step 3.4: After the high voltage thyristor is turned off, the off-time compensation branch switch is turned off; Step 3.5: When the low-voltage thyristor is subjected to a forward voltage, the RC branch switch is closed to charge the capacitor until the capacitor is fully charged and then disconnected.

[0008] The beneficial effects of the present invention are as follows: by analyzing the characteristics of carrier changes during the turn-off process of the thyristor, the core device of the converter, the differences in the turn-off characteristics of thyristors of different voltage levels are compared, and a physical equivalent method of parallel compensation branches at both ends of low-voltage and low-current thyristors is proposed in a targeted manner. Compared with the existing thyristor physical equivalent method, the method of the present invention compensates for the reverse recovery current of the low-voltage thyristor by discharging the capacitor in the RC branch, ensuring that the reverse recovery current peak value of the model thyristor is the same as that of the actual thyristor. I RMThe consistency of the model thyristor and the prototype thyristor is improved, which improves the simulation accuracy of important parameters in the thyristor turn-off process. At the same time, by using a bidirectional switch to transfer the loop current to the turn-off time compensation branch after the low-voltage thyristor is turned off, the turn-off time of the model thyristor is indirectly increased, which makes up for the neglect of the thyristor turn-off time in the existing physical equivalent method, thereby achieving dynamic consistency of the nonlinear switching characteristics of the model thyristor and the prototype thyristor. At the same time, a method for selecting parameters of each component in the physical equivalent model and a switch switching method are proposed to ensure the accuracy of the equivalence of the turn-off characteristics of the model thyristor to the prototype thyristor, and realize the accurate simulation of the turn-off process of the actual thyristor under different operating conditions, which greatly improves the accuracy of the physical model. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings described herein are used to provide further understanding of the present invention and constitute a part of this application. The illustrative examples of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0010] Figure 1 It is a schematic diagram of the internal structure of the thyristor of the present invention; Figure 2 It is a schematic diagram of voltage and current changes during the thyristor commutation and blocking capability recovery process of the present invention; Figure 3 It is a schematic diagram of the electric field and carrier dynamic process during the thyristor turn-off process of the present invention; Figure 4 This is a comparison diagram of reverse recovery of thyristors of different voltage levels according to the present invention; Figure 5 It is a schematic diagram of the physical equivalent model of the thyristor of the present invention; Figure 6 It is an equivalent circuit diagram after the compensation branch of the present invention is turned on; Figure 7 It is a logic block diagram of the working principle of the thyristor physical model of the present invention; Figure 8 , Fig. 9 The figure is a comparison chart of the simulation accuracy between the existing physically equivalent low-voltage thyristor and the present invention. DETAILED DESCRIPTION

[0011] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0012] See also Figures 1 to 9 As shown, the thyristor physical equivalent simulation method considering the nonlinear switching transient characteristics of the present invention first studies the carrier change law during the thyristor turn-off process, analyzes the turn-off mechanism of the thyristor, compares the turn-off characteristics of thyristors of different voltage levels, and proposes a thyristor physical equivalent method that connects a full-controlled switch loop in parallel at both ends of a low-voltage and low-current thyristor to compensate for the turn-off characteristics difference between the two. A thyristor physical equivalent model that ensures the consistency of the nonlinear switching transient characteristics of thyristors of different voltage levels is established, a method for selecting parameters of each component of the model is proposed, and a switch switching method is designed to achieve the consistency of the dynamic process of the turn-off characteristics of the model thyristor and the prototype thyristor. The specific process is as follows: 1. Analysis of thyristor turn-off characteristics and turn-off mechanism The internal structure diagram of the thyristor is as follows Figure 1 As shown, it is divided into four layers, which are composed of four semiconductors with different doping arranged alternately, forming a PN junction between every two semiconductors. + The cathode layer, from which the cathode K is drawn; the second layer is the P base region, from which the gate G is drawn; the third layer is the lightly doped N − The base region is wider than other layers in order to improve the voltage resistance of the device. The last layer is a semiconductor with P-type doping, from which the anode A of the thyristor is led out.

[0013] 1.1 Analysis of thyristor carrier change during the turn-off process The voltage and current changes during the thyristor switching and blocking capacity recovery process are as follows: Figure 2 As shown, where: i T is the current flowing through the thyristor; U T is the voltage across the thyristor; I F is the forward current; I RM is the reverse recovery current peak; U R is the reverse external voltage; U RM is the maximum reverse voltage; I co is the off-state leakage current of the thyristor. t 1~ t The reverse recovery current flowing through the thyristor increases from zero to peak value in the 3rd stage I RM , called storage time t s ; t 3~ t 4-stage reverse recovery current from IRM Decays exponentially to 0.1 I RM , called the fall time t f ;Reverse recovery time t rr is the sum of the two; t 4~ t The reverse recovery current in stage 5 decreases very slowly until it reaches 0, which is called the forward blocking recovery time. t gt ;Reverse recovery time t rr Forward Blocking Recovery Time t gt The sum of the two is called the turn-off time of the thyristor, recorded as t q .

[0014] The thyristor turn-off process is essentially a process in which most of the charges remaining in the base region are dissipated through various motions after the conduction process. The carriers remaining in the base region after the conduction process are mainly non-equilibrium carriers. Since the non-equilibrium carriers are preferentially injected into the low-concentration doped region in the conduction state, N - The non-equilibrium carriers in the base region play a major role in the recovery of blocking ability.

[0015] The internal carrier dissipation characteristics of the thyristor during the turn-off process are mainly affected by N - The influence of the concentration difference between non-equilibrium carriers and equilibrium carriers in the base region: When the concentration of non-equilibrium carriers is much higher than that of equilibrium carriers, the whole process can be regarded as the migration of charge from the dielectric to the electrode at the electrode-dielectric electrical contact interface. At this time, a large current flows through the thyristor, and the carriers move out of the thyristor along with the large current. This process is usually called the sweep-out process; when the concentration of non-equilibrium carriers is slightly higher or lower than that of equilibrium carriers, the remaining non-equilibrium carriers dissipate in the form of electron and hole neutralization. This process is usually called the recombination process. For the convenience of analysis, the carrier sweep-out rate and carrier recombination rate are used to describe the carrier sweep-out and recombination processes respectively.

[0016] The changes in the dissipation forms of the carriers in the thyristor such as sweeping out and recombination during the turn-off process are closely related to the characteristics of the three equivalent PN junctions J1, J2 and J3. By analyzing the changes in the electric field and equivalent PN junctions in the thyristor during the turn-off process, it is helpful to analyze the changes in the dynamic dissipation process of the carriers, and then determine the segmentation basis of the turn-off model. The schematic diagram of the electric field and carrier dynamic process in the thyristor turn-off process is shown in the figure. Figure 3 shown.

[0017] by Figure 2Take the example to illustrate the dynamic dissipation characteristics of thyristor carriers and the changes of equivalent PN junction during the turn-off process: by t Time 0 is the starting time of the thyristor commutation process. t At time 1, the current reverses through zero, which is regarded as the beginning of the shutdown process; t 1~ t In the 2nd stage, J1, J2 and J3 are all in the forward bias state, and the P region and N - A large number of carriers stored in the N region are swept out as the reverse current increases; at the same time, due to the - The doping concentration of the P region is low, and the P region and N - The recombination process of electrons and holes between regions gradually accelerates. In this process, the carriers in the P region decay rapidly, causing the J3 junction storage carriers to decay to zero first, and J3 changes from forward bias to reverse bias. R sh The reverse blocking capability is restored under the action of . The carrier dissipation characteristics at this stage are that the sweep-out process and the recombination process are carried out simultaneously, and the carrier sweep-out rate is much greater than the carrier recombination rate. The sweep-out process is the main carrier dissipation process of the thyristor.

[0018] t 2~ t In stage 3, after J3 is reverse biased, both ends of the thyristor begin to bear reverse voltage. Since J3 is a heavily doped PN junction, the reverse voltage immediately rises to the avalanche breakdown voltage of J3 (about 20V), and J3 is broken down. The time from J3 being reverse biased to being broken down is very short, so its process is often ignored in the analysis process. After J3 is broken down, the carriers continue to be swept out and recombined with the reverse current, and the carriers stored in the J1 junction with a lower doping degree gradually decay to zero. At this time, J1 changes from forward bias to reverse bias, begins to bear reverse voltage and restores reverse blocking ability. At this time, the space charge region formed by the reverse bias of J1 hinders the carrier sweeping process, and the carrier sweeping rate gradually decreases. After J3 and J1 are reverse biased, the thyristor in this working state is similar to a PNP transistor with a floating base. At this time, the dissipation of carriers is mainly affected by N - Control of carrier recombination process in the base region.

[0019] t 3~ t In stage 5, after the reverse recovery current reaches its peak value, the residual carrier concentration inside the thyristor is low, and the thyristor is in a small injection state. In the falling stage and the forward blocking recovery stage, the concentration difference between the non-equilibrium carriers and the equilibrium carriers is too small, resulting in the inability to continue to sweep out the carriers in the base region. The carriers continue to dissipate in the recombination process. The specific dissipation process can be approximately described by an exponential model with the minority carrier lifetime as the time constant.

[0020] In the formula is the original carrier concentration before the carrier recombination process, is the minority carrier lifetime. is the average time it takes for electrons and holes to recombine in silicon, It is logarithmically related to the carrier recombination rate, and its value is related to the thyristor storage time. t s The value of is close, that is

[0021] From the definition of minority carrier lifetime, it can be seen that minority carrier lifetime is negatively correlated with the carrier recombination rate of thyristor.

[0022] 1.2 Analysis of thyristor turn-off mechanism Current zero-crossing rate of change d i / d t , forward current I F and junction temperature T j It is a key factor affecting the turn-off characteristics of the thyristor and the dynamic characteristics of the carriers. By analyzing the relationship between the above factors affecting the turn-off characteristics and the original carrier concentration, the carrier sweep rate and the carrier recombination rate, it can be obtained that the current zero-crossing rate of change d i / d t Mainly affects the carrier sweep rate; forward current I F Mainly affects the original carrier concentration; junction temperature T j It mainly affects the carrier recombination rate. i / d t , I F as well as T j It is the key factor affecting the turn-off characteristics of the thyristor. i / d t , I F , T j Key factors affecting , I RM , t rr , t q The influence of the core recovery parameters that characterize the turn-off characteristics is then used to analyze the thyristor turn-off mechanism in combination with the carrier dissipation theory.

[0023] When the thyristor current passes through zero, the rate of change d i / d tWhen the carrier density and carrier recombination rate are increased, the original carrier concentration and carrier recombination rate remain basically unchanged, and the carrier sweep rate increases. This results in the thyristor switching time, i.e. Figure 2 middle t 0~ t 1 period becomes shorter. Therefore, the amount of carriers dissipated due to carrier recombination during the commutation period decreases. t At time 1, the residual carrier concentration of the thyristor increases, resulting in the reverse recovery charge of the thyristor. Reverse recovery current peak I RM Increase, and at the same time, the reverse recovery process is accelerated due to the increase in the carrier sweep rate, and the reverse recovery time t rr The reduction of reverse recovery time leads to an increase in the residual carrier concentration in the base region when the forward blocking recovery process begins, and the forward blocking recovery time t gt increases, thus making the entire off time t q Increase.

[0024] When the forward current I F When it increases, the carrier sweep rate and carrier recombination rate remain unchanged, the original carrier concentration increases, and the thyristor switching time remains unchanged. t At time 1, the carrier concentration of the thyristor increases, resulting in the reverse recovery charge of the thyristor. , reverse recovery current peak I RM Increase, reverse recovery time t rr Increase, turn-off time t q Increase.

[0025] When the thyristor junction temperature T j When the carrier concentration increases, the carrier sweep rate remains unchanged, the original carrier concentration and the carrier recombination rate increase, and the thyristor switching time remains unchanged. The increase in the original carrier concentration leads to the reverse recovery charge , reverse recovery current peak I RM And reverse recovery time t rr The reverse recovery charge increases; the carrier recombination rate increases, resulting in , reverse recovery current peak I RM And reverse recovery time t rr In this case, the effect of the increase in the original carrier concentration is greater than the effect of the increase in the carrier recombination rate. tAt time 1, the carrier concentration of the thyristor increases, resulting in the reverse recovery charge of the thyristor. , reverse recovery current peak I RM Increase, reverse recovery time t rr Increase, turn-off time t q Increase.

[0026] 2. Physical equivalent method of thyristor considering nonlinear switching characteristics 2.1 Analysis of the difference in turn-off characteristics of thyristors at different voltage levels Although the structures of thyristors of the same model and different voltage levels are the same, their internal carrier doping concentrations are different, which is the fundamental reason for the difference in their physical properties. As the voltage level increases, the turn-off time of the thyristor increases. t rr , reverse recovery current peak I RM Parameters such as will increase accordingly, resulting in obvious differences in the reverse recovery process of thyristors of different voltage levels, such as Figure 4 The figure shows the difference in reverse recovery current between high voltage level and low voltage level thyristors.

[0027] The blue curve in the figure is the reverse recovery current curve of the high voltage thyristor, and the red curve is the reverse recovery current curve of the low voltage thyristor. I FH and I FL are the forward conduction currents of high voltage and low voltage thyristors respectively; I RMH and I RML are the reverse recovery current peaks of high voltage and low voltage thyristors respectively; t H and t L The turn-off time of high voltage and low voltage thyristors respectively. If two voltage level thyristors are used in the converter, at the same switching time t r Under the action of, the two will undergo different physical processes due to the difference in shutdown characteristics, which can be divided into the following three situations: 1) When the commutation time t r Shorter than low voltage thyristor turn-off time t LAt this time, both voltage level thyristors will be subjected to forward voltage when they are not completely turned off, and there are still residual carriers inside the thyristors, so both thyristors will be turned on again, resulting in commutation failure of the converter.

[0028] 2) When the commutation time t r Greater than the high voltage thyristor turn-off time t H At this time, both thyristors are completely turned off when subjected to the forward voltage, and the carriers inside the thyristors have all dissipated. Therefore, the thyristors of both voltage levels will not be turned on again, and the converter will not fail in commutation.

[0029] 3) When the switching time t r Between t L and t H In the meantime, the high-voltage thyristor has not been completely turned off when subjected to the forward voltage, and there are a small amount of carriers inside. The high-voltage thyristor will be turned on again, resulting in a commutation failure in the converter. The low-voltage thyristor has been completely turned off when subjected to the forward voltage, and there are no carriers inside. The low-voltage thyristor will continue to remain in the off state, and the converter will not fail to commutate. There is a difference in the physical processes experienced by the two under this working condition.

[0030] 2.2 Construction of thyristor physical equivalent model By comparing the three different situations, we can see that due to the difference in turn-off characteristics, the two voltage level thyristors may undergo different physical processes when encountering the same operating conditions. This also proves that it is impossible to use a single proportional reduction method to make the thyristors physically equivalent. In order to make up for this difference, based on the above analysis of the thyristor turn-off characteristics, a thyristor physical equivalent model is proposed in which a fully controlled switch circuit is connected in parallel at both ends of the low-voltage and low-current thyristor to compensate for the difference in the turn-off time between the two. The model schematic diagram is shown in the figure. Figure 5As shown. The model contains two branches, one is the reverse recovery current compensation branch with resistors, capacitors and bidirectional switches in series, and the other is the turn-off time compensation branch with only bidirectional switches in series. The working principle of the model is that when two voltage level thyristors are turned on, the reverse recovery current of the high voltage level thyristor will be greater than the reverse recovery current of the low voltage level thyristor. At this time, the reverse recovery current of the low voltage level thyristor is compensated by the resistor-capacitor branch in the model, and the reverse recovery current deviation of the two is corrected by capacitor discharge. When the reverse recovery current of the high voltage level thyristor reaches its peak, the branch is disconnected to stop compensating the reverse recovery current of the low voltage level thyristor. Since the turn-off time of low-voltage thyristors is shorter than that of high-voltage thyristors, low-voltage thyristors will be turned off before high-voltage thyristors. At this time, the turn-off time compensation branch in the model comes into play. It will transfer the current in the loop to the turn-off time compensation branch to simulate the reverse recovery process of the thyristor, thereby indirectly increasing the turn-off time of the low-voltage thyristor. When the high-voltage thyristor is turned off, the turn-off time compensation branch is disconnected. At this time, both voltage-level thyristors are completely turned off and the forward blocking effect is restored, ensuring that the turn-off characteristics of the two are dynamically consistent.

[0031] 2.3. Method for selecting parameters of thyristor physical model The thyristor model is mainly composed of low voltage thyristors, RC branches and bidirectional switches. Figure 2 It can be seen that the turn-off process of the thyristor can be divided into three stages, among which t 1~ t 3 is the reverse recovery current at a constant rate d i / d t During the process of increasing, the reverse recovery current can be expressed as:

[0032] in I R is the reverse recovery current flowing through the thyristor, I F is the forward conduction current of the thyristor, d i / d t is the current change rate, which can be expressed as:

[0033] in U VT is the voltage across the thyristor, L is the equivalent capacitance value of the branch where the thyristor is located, so the reverse recovery current flowing through the thyristor can be expressed as:

[0034] The difference in reverse recovery current between high voltage thyristor and low voltage thyristor is:

[0035] in, I R is the reverse recovery current difference, the subscript H represents the high voltage thyristor parameter, and the subscript L represents the low voltage thyristor parameter. Assume that the difference between the high voltage thyristor and the low voltage thyristor is K times, then equation (2-4) can be expressed as:

[0036] like Figure 6 As shown in the figure, it is the equivalent circuit diagram after the RC compensation branch in the thyristor model is turned on, where U C is the voltage across the capacitor, U R is the voltage across the resistor, i r is the RC branch current, i VT is the current flowing through the low voltage thyristor. According to the equivalent circuit diagram, the differential equation can be written as follows:

[0037] The compensation branch current i r It can be expressed as:

[0038] Then formula (2-6) can be expressed as:

[0039] At the same time, if you want to achieve non-compensation for the reverse recovery current of thyristors of different voltage levels, the size of the compensation branch circuit should be equal to the difference in reverse recovery current of thyristors of different voltage levels, which can be expressed as:

[0040] Finally, combine equations (2-9) and (2-10), substitute the known physical quantities to solve the differential equation, and you can get the capacitance value in the resistance-capacitance compensation path. C and resistance value R .

[0041] 2.4. Thyristor physical model switch switching method After completing the calculation of the physical model parameters of the thyristor, it is necessary to use the device manual and mathematical model to calculate the reverse recovery characteristic parameters of the high-voltage thyristor and the low-voltage thyristor before the experiment, compare the differences between the parameters of the two, and form a switch trigger table to trigger the model switch. Only by switching at different stages of the two thyristor shutdown process can the dynamic consistency of the shutdown characteristics of the two be achieved. The specific switch switching method is as follows: 1) When the two voltage level thyristors begin to bear reverse voltage, they will enter the reverse recovery current increase stage. At this time, the T1 switch of S1 is turned on, and the capacitor discharge is used to compensate for the deviation of the reverse recovery current of the low voltage thyristor; 2) After a period of time, when the reverse recovery current of the low voltage thyristor reaches its peak value, the T1 switch of S1 is disconnected to stop compensating for the reverse recovery current; 3) When the low-voltage thyristor is completely turned off, the T2 switch of S2 is turned on. At this time, the loop current will be transferred from the thyristor branch to the S2 branch, simulating the off state of the thyristor and indirectly increasing the equivalent off time of the thyristor model; 4) When the high voltage level thyristor is completely turned off, the T2 switch of S2 is disconnected. At this time, there will be no current in the model and the model thyristor is in the off state; 5) When the model thyristor is subjected to a forward voltage, the switch T2 of S1 is turned on and begins to charge the capacitor; 6) When the capacitor is fully charged, the switch T2 of S1 is disconnected.

[0042] The above is the complete working process of the thyristor model. It uses the capacitor discharge in the RC resistor-capacitor branch to compensate for the difference between the reverse recovery current of the model thyristor and the actual high-voltage thyristor. At the same time, the S2 branch is used to transfer the current originally flowing through the low-voltage thyristor to the S2 branch to achieve the compensation of the turn-off time. The model is equivalent to the physical characteristics of the actual thyristor to the greatest extent. The specific working principle logic block diagram of the model is as follows Figure 7 shown.

[0043] Thyristor physical model accuracy verification: Embodiment 1: The high voltage thyristor actually operates at a forward current I F =2000A, and a forward voltage is applied at 195μs to trigger the thyristor; the existing physical equivalent low-voltage thyristor and the low-voltage thyristor model proposed in the present invention operate at a forward current I F=200A, the forward voltage is also applied at 195μs to trigger the thyristor. By observing the operating states of the three thyristors when triggered, the simulation accuracy of the existing physical equivalent low-voltage thyristor and the low-voltage thyristor proposed in the present invention is compared. The specific experimental results are as follows: Figure 8 shown.

[0044] Depend on Figure 8 It can be seen that the high-voltage thyristor and the low-voltage thyristor of the physical simulation method proposed in the present invention are both turned on under the action of the forward voltage, while the low-voltage thyristor of the existing physical simulation method has restored its blocking ability and has not been turned on again. This proves that the thyristor model proposed in the present invention accurately simulates the actual thyristor's turn-off process and the physical change process when triggered. The accuracy of the present invention is better than that of the existing thyristor physical equivalent method.

[0045] Embodiment 2: The high voltage thyristor actually operates at a forward current I F =2000A, and a forward voltage is applied at 285μs to trigger the thyristor; the existing physical equivalent low-voltage thyristor and the low-voltage thyristor model proposed in the present invention operate at a forward current I F =200A, the forward voltage is also applied at 285μs to trigger the thyristor. By observing the operating states of the three thyristors when triggered, the simulation accuracy of the existing physical equivalent low-voltage thyristor and the low-voltage thyristor proposed in the present invention is compared. The specific experimental results are as follows: Fig. 9 shown.

[0046] Depend on Fig. 9 It can be seen that all three thyristors maintained the forward blocking state when triggered by the forward voltage at 285μs, but the thyristor model proposed in the present invention is closer to the actual parameters of high-voltage thyristors than the existing thyristor model in terms of various reverse recovery parameters. This proves that the thyristor model proposed in the present invention accurately simulates the turn-off process of the actual thyristor and the dynamic change process of various parameters when triggered. The accuracy of the present invention is better than the existing thyristor physical equivalent method.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made to the present invention shall be included in the protection scope of the present invention.

Claims

1. A physical equivalent simulation method for thyristors considering the transient characteristics of nonlinear switches, characterized in that: The steps include: Step 1: Correct the differences between the turn-off characteristics of thyristors of different voltage levels, and establish a thyristor physical model that achieves consistent nonlinear switching transient characteristics of thyristors of different voltage levels; Step 1.1: Compare the forward conduction current of thyristors with different voltage levels I F , reverse recovery current peak I RM And the off time t rr , analyze the differences between the turn-off characteristics of thyristors at different voltage levels; Step 1.2: Analyze system commutation time t r Thyristor turn-off time with low voltage level t L , high voltage thyristor turn-off time t H The influence of the relationship between the three on the commutation process; Step 1.3: Establish a physical model of the thyristor, use a parallel damping branch to compensate for the reverse recovery current of the thyristor, and switch the switch by judging the direction of the voltage across the thyristor; Step 2: Select the parameters of the resistor and capacitor in the RC branch of the thyristor physical model; Step 3: According to the different stages of the high voltage thyristor turn-off process, a switch switching method is adopted to achieve consistent turn-off characteristics of thyristors of different voltage levels.

2. The thyristor physical equivalent simulation method considering the transient characteristics of nonlinear switches according to claim 1 is characterized in that: The parameters of the resistor and capacitor in the RC branch of the thyristor physical model described in step 2 are selected as follows: Step 2.1: By comparing the reverse recovery current differences of thyristors with different voltages, the parameters of the capacitor C in the RC branch are determined to compensate for the reverse recovery current differences; Step 2.2: Determine the parameters of the resistor R in the branch according to the maximum current that the RC branch can withstand.

3. The thyristor physical equivalent simulation method considering the transient characteristics of nonlinear switches according to claim 1, characterized in that: According to the different stages of the high voltage thyristor turn-off process, the switch switching method is adopted in step 3 to achieve the same turn-off characteristics of thyristors of different voltage levels, specifically: Step 3.1: When the high voltage thyristor enters the reverse recovery current increasing stage, the RC branch switch is turned on, and the capacitor discharge is used to compensate for the reverse recovery current difference; Step 3.2: When the reverse recovery current of the high voltage thyristor reaches a peak value, the RC branch cut-off switch is turned off; Step 3.3: After the low voltage thyristor is turned off, the off time compensation branch switch is turned on, so that the current is transferred to the branch, indirectly extending the off time of the low voltage thyristor; Step 3.4: After the high voltage thyristor is turned off, the off-time compensation branch switch is turned off; Step 3.5: When the low-voltage thyristor is subjected to a forward voltage, the RC branch switch is closed to charge the capacitor until the capacitor is fully charged and then disconnected.

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