Custom thyristor digital modeling method considering reverse turn-off characteristics

Abstract

The application relates to a self-defined thyristor digital modeling method considering reverse blocking characteristics, and belongs to the field of traditional high-voltage direct current transmission. The method comprises a thyristor model, a controllable current source, a fitting parameter calculation module, a reverse blocking recovery module and a forward blocking recovery module of a power system digital simulation software. The fitting parameter calculation module is used to obtain parameters required by fitting functions in the reverse blocking and forward blocking recovery modules under different junction temperatures, when it is detected that the current flowing through the software self-defined thyristor model is reduced to zero, the reverse recovery module is started, the thyristor enters a reverse recovery stage, and the controllable current source is controlled to output a reverse recovery current in real time. The forward blocking recovery module is used to simulate the forward blocking recovery characteristics of the thyristor. The application considers the change of the junction temperature of the thyristor and the forward blocking recovery process, can provide a more accurate simulation model for related research work of commutation failure, and has practical significance for the research of resisting commutation failure.

Description

Technical Field

[0001] This invention relates to the field of high-voltage direct current transmission, and in particular to a custom thyristor digital modeling method that considers reverse turn-off characteristics. This method can reflect the actual turn-off characteristics of thyristors and provide a more accurate simulation model for research on commutation failure. Background Technology

[0002] Traditional high-voltage direct current (HVDC) transmission technology boasts advantages such as high transmission capacity and good economic efficiency, making it widely used in HVDC transmission projects. The core component of the HVDC converter is the semi-controlled high-power thyristor, whose operating characteristics determine the performance of the HVDC transmission system. When a conducting thyristor is subjected to reverse voltage, it undergoes a turn-off process. This process is often a vulnerable point that can lead to thyristor overvoltage damage or HVDC commutation failure. However, the thyristor model provided by commonly used power system digital simulation software is a switch model based on a variable resistor, neglecting its reverse turn-off characteristics and assuming that thyristor conduction and turn-off can be completed instantaneously. Therefore, the built-in model cannot reflect the converter valve characteristics under actual operating conditions, resulting in significant simulation errors. For refined simulation analysis of the commutation process, research on digital simulation models that consider the thyristor turn-off characteristics is particularly important.

[0003] Currently, there is some research on modeling thyristor turn-off characteristics both domestically and internationally. Some researchers have proposed macro-models of thyristors considering secondary effects, and others have proposed adding a reverse recovery module to the macro-model to describe the reverse recovery characteristics of thyristors. Still others have proposed using nonlinear power sources, natural growth curves, exponential functions, and hyperbolic secant functions to reflect the turn-off characteristics of thyristors. However, research mainly focuses on the reverse recovery blocking characteristics of thyristors, neglecting the forward blocking recovery characteristics and the influence of junction temperature variations on the turn-off characteristics. Therefore, it is necessary to establish a custom thyristor digital model that can reflect the entire turn-off process at different junction temperatures, thereby providing a more accurate simulation model for research on commutation failure. Summary of the Invention

[0004] The purpose of this invention is to provide a custom digital modeling method for thyristors that considers reverse turn-off characteristics, solving the technical problems of existing thyristor simulation models failing to reflect forward blocking recovery and difficulties in representing junction temperature. This invention, based on the built-in thyristor model in power system digital simulation software, adds a controllable current source in parallel and includes modules for calculating fitting parameters, reverse blocking recovery, and forward blocking recovery to perform complete thyristor modeling.

[0005] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0006] A custom thyristor digital modeling method considering reverse turn-off characteristics includes the following steps:

[0007] Step (1) Construction of the fitting parameter calculation module;

[0008] Step (2) Construction of the thyristor reverse blocking recovery module;

[0009] Step (3) Construction of the thyristor forward blocking recovery module.

[0010] The fitting parameter calculation module in step (1) is divided into two parts. One part is to calculate the zero-crossing current change rate di / dt and the peak value of the positive current I. F The other part involves calculating the fitting coefficients of the fitting functions in the reverse recovery blocking module and the forward recovery blocking module at different junction temperatures.

[0011] The reverse blocking recovery module described in step (2) outputs the reverse recovery current in real time. It starts when the current flowing through the thyristor model in the power system digital simulation software decreases to zero, and the thyristor enters the reverse recovery phase. The time t1 when the forward conduction current of the thyristor decreases to zero is obtained through sample-and-hold. In the reverse blocking recovery module, the thyristor reverse recovery characteristic curve is represented by an exponential function. The value of the key parameter time constant τ in the exponential function expression is calculated using a fitting function method. Then, the time t2 when the reverse recovery current reaches its peak value is determined through relational operators and sample-and-hold. Finally, the exponential form of the reverse recovery current value at different junction temperatures is calculated in real time. The exponential function is expressed as:

[0012]

[0013] In equation (1), the time constant τ is

[0014]

[0015] The fitting function Q in equation (2) rr and I RM for

[0016] Q rr =α0+α1di / dt+α2I F (3)

[0017] I RM =β0+β1di / dt+β2I F (4)

[0018] In the formula, t1 is the moment when the forward conduction current of the thyristor decreases to zero, di / dt is the rate of change of the zero-crossing current corresponding to time t1, t2 is the moment when the reverse recovery current reaches its peak value, and I RM Q is the peak value of the reverse recovery current. rr To recover the charge in the reverse direction, I FThe peak value of the forward current is given, τ is the time constant, and α0, α1, and α2 are the values ​​of Q. rr With di / dt, I F The fitting coefficients obtained between them, β0, β1, β2 are I RM With di / dt, I F The fitting coefficients obtained between them.

[0019] The forward blocking recovery module described in step (3) simulates the structural composition of the forward blocking recovery characteristics of a thyristor. The forward blocking recovery module obtains the minimum turn-off time t at different junction temperatures through a fitting function. q Its function is as follows: when a forward voltage is detected on the thyristor during the minimum turn-off time (i.e., before the forward blocking capability is restored), the thyristor immediately turns on; conversely, when the forward blocking capability is restored, the thyristor needs to be triggered normally to turn on. The fitted function t... q for:

[0020]

[0021] In the formula, t q I is the turn-off time, di / dt is the rate of change of current at the zero-crossing point, and I is the turn-off time. F For the positive current peak, λ0, λ1, and λ2 are t q With di / dt, I F The fitting coefficients obtained between them.

[0022] The beneficial effects of this invention are as follows: This invention establishes a custom thyristor model that can reflect the reverse blocking recovery process and the forward blocking recovery process of a thyristor at different junction temperatures, thus overcoming the shortcoming of the built-in thyristor model in power system digital simulation software that ignores its turn-off characteristics. The actual turn-off time of a thyristor varies with changes in external operating conditions and environment, while the turn-off time t set in the built-in thyristor model of power system digital simulation software is inconsistent. q A custom thyristor model compensates for this shortcoming by using a fixed value. Furthermore, during the turn-off time (i.e., before the thyristor regains its forward blocking capability), the custom thyristor model detects a forward voltage and turns on the thyristor; conversely, when the forward blocking capability is lost, the thyristor regains its forward blocking capability and requires normal triggering to turn on. The established model reflects the actual characteristics of the thyristor. This model can be used in thyristor converters to construct a refined electromagnetic transient model of the converter considering the device turn-off characteristics, providing a more accurate simulation model for research on commutation failure. Attached Figure Description

[0023] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate the invention and are used to explain it, but do not constitute an undue limitation of the invention.

[0024] Figure 1 This is a schematic diagram of the custom complete thyristor modeling of the present invention;

[0025] Figure 2 This is a schematic diagram of the fitting parameter calculation module of the present invention;

[0026] Figure 3 This is a schematic diagram of the thyristor reverse blocking recovery module of the present invention;

[0027] Figure 4 This is a schematic diagram of the thyristor forward blocking recovery module of the present invention;

[0028] Figure 5 This is a schematic diagram of an embodiment of the present invention (I). RM (Comparison chart of simulated and measured values);

[0029] Figure 6 This is a schematic diagram of an embodiment of the present invention (t) q (Comparison chart of simulated and measured values);

[0030] Figure 7 This is a schematic diagram of an embodiment of the present invention (t) q (Schematic diagram of applying a positive voltage to a custom thyristor model);

[0031] Figure 8 This is a schematic diagram of an embodiment of the present invention (t) q (Schematic diagram of applying a positive voltage to a custom thyristor model). Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] See Figures 1 to 4As shown, the present invention provides a custom thyristor digital modeling method considering reverse turn-off characteristics. Its structure includes a thyristor model integrated into power system digital simulation software, a controllable current source, a fitting parameter calculation module, a reverse blocking recovery module, and a forward blocking recovery module. The fitting parameter calculation module calculates the parameters required for the fitting functions in the reverse blocking and forward blocking recovery modules at different junction temperatures. When the current flowing through the software's built-in thyristor model decreases to zero, the reverse recovery module is activated, and the thyristor enters the reverse recovery phase, controlling the controllable current source to output the reverse recovery current in real time. The forward blocking recovery module simulates the thyristor's forward blocking recovery characteristics. This invention considers the changes in thyristor junction temperature and the forward blocking recovery process, providing a more accurate simulation model for research on commutation failure and having practical significance for research on mitigating commutation failure.

[0034] See Figure 1 The diagram shown illustrates a custom thyristor model. The digital modeling method for a custom thyristor, considering reverse turn-off characteristics, of this invention mainly includes the following steps:

[0035] 1) By adding a controllable current source in parallel to the built-in thyristor model in the power system digital simulation software, and by adding a fitting parameter calculation module, a reverse blocking recovery module, and a forward blocking recovery module, a complete thyristor model is created. This solves the problem that existing thyristor simulation models cannot reflect their forward blocking recovery. In the figure, A, K, and G are the anode, cathode, and control electrode of the custom thyristor model, respectively, and m is the measurement port of the built-in thyristor model in the simulation software, measuring the current i flowing through it. AK and the voltage drop across both ends u AK The measured current i AK The junction temperature is directly input and applied to the fitting parameter calculation module based on the actual test conditions of the thyristor.

[0036] 2) Figure 2 This is a schematic diagram of the fitting parameter calculation module. Based on the information from step 1), the zero-crossing current change rate di / dt and the peak forward current I of the thyristor are obtained through relational operators, differential operations, and sample-and-hold operations. F Junction temperature T j It is set directly based on the actual test conditions of the thyristor, via T j The fitting coefficients α, β, and λ were obtained by selecting measured data at different junction temperatures, where α is the coefficient of Q. rr With di / dt, I F The fitting coefficients α0, α1, α2, and β obtained from the fit between are I. RM With di / dt, I F The fitting coefficients β0, β1, and β2 obtained between them, and λ is t q With di / dt, I FThe fitting coefficients λ0, λ1, and λ2 are obtained by fitting between them.

[0037] 3) Figure 3 A schematic diagram of the thyristor reverse blocking recovery module is provided, combined with... Figure 1 and Figure 3 When the current flowing through the thyristor model decreases to zero, the reverse blocking recovery module is activated, and the thyristor enters the reverse recovery phase. The moment t1 when the forward conduction current of the thyristor decreases to zero is obtained through sample-and-hold. Based on step 2), the peak value of the reverse recovery current I is calculated through three function modules. RM Reverse recovery charge Q rr The value of the time constant τ in the exponential function. The time t2 when the reverse recovery current reaches its peak is determined using relational operators and sample-and-hold. At time t2, the exponential calculation module starts, calculating the exponential form of the reverse recovery current value at different junction temperatures in real time. Module 1 is used to switch the output of the reverse recovery current before and after time t2. The reverse blocking recovery module directly outputs the dynamic value of the reverse recovery current after the thyristor current drops below zero using a mathematical expression. This value is applied to a controllable current source, reflecting the reverse blocking recovery process of the thyristor in real time. The exponential function is expressed as:

[0038]

[0039] In equation (1), the time constant τ is

[0040]

[0041] The fitting function Q in equation (2) rr and I RM for

[0042] Q rr =α0+α1di / dt+α2I F (3)

[0043] I RM =β0+β1di / dt+β2I F (4)

[0044] In the formula, t1 is the moment when the forward conduction current of the thyristor decreases to zero, di / dt is the rate of change of the zero-crossing current corresponding to time t1, t2 is the moment when the reverse recovery current reaches its peak value, and I RM Q is the peak value of the reverse recovery current. rr To recover the charge in the reverse direction, I F The peak value of the forward current is given, τ is the time constant, and α0, α1, and α2 are the values ​​of Q. rr With di / dt, I F The fitting coefficients obtained between them, β0, β1, β2 are I RM With di / dt, IF The fitting coefficients obtained between them.

[0045] 4) Figure 4 A schematic diagram of the thyristor forward blocking recovery module is provided. Combining steps 2) and 3), the minimum turn-off time t at different junction temperatures is obtained through equation (5). q When a forward voltage is detected on the thyristor during its minimum turn-off time (i.e., before it recovers its forward blocking capability), selection module 2 switches to input a high-level signal to the thyristor's control electrode, at which point the thyristor turns on. Conversely, when the forward blocking capability is restored, the thyristor returns to its forward blocking capability and requires normal triggering to turn on. (Fitting function t) q for:

[0046]

[0047] In the formula, t q I is the turn-off time, di / dt is the rate of change of current at the zero-crossing point, and I is the turn-off time. F For the positive current peak, λ0, λ1, and λ2 are t q With di / dt, I F The fitting coefficients obtained between them.

[0048] Taking the Zhuzhou CRRC KPc2000-85Y02 thyristor as an example, according to the thyristor test conditions, the junction temperature is set to 90℃ and the capacitor charging voltage to 200V. By changing the circuit inductance, capacitance, and the time value of the applied forward voltage, the turn-off characteristic curves of different zero-crossing current change rates under a certain forward current peak are obtained. The forward current peak is set to 2000A. The simulation values ​​and measured values ​​of the reverse recovery current peak and turn-off time during the turn-off process of the custom thyristor model are compared. Figure 5 and Figure 6 As shown.

[0049] The junction temperature was set to 90℃, the capacitor charging voltage to 200V, the peak forward current to 2000A, and the zero-crossing current change rate to 2A / μs. Under these operating conditions, a forward voltage was applied to the thyristor during the turn-off time to verify its forward blocking and recovery characteristics. The simulation results are as follows: Figure 7 and Figure 8 As shown.

[0050] Depend on Figure 5 and Figure 6 The data comparison shows that the error between the simulated and measured values ​​of the reverse recovery current peak value remains within 5%, and the error between the simulated and measured values ​​of the turn-off time remains within 4%. Figure 7 This means that outside the turn-off time, after the thyristor has recovered from forward blocking, a forward voltage is applied to the custom thyristor model, and the thyristor turns on according to the normal conduction conditions. Figure 8This indicates that when a positive voltage is applied to the custom thyristor model during the turn-off time, the custom model immediately turns on. Simulations show that the established digital thyristor model can effectively reflect the device's turn-off characteristics and more accurately simulate the thyristor's turn-off process.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made to the present invention should be included within the scope of protection of the present invention.

Claims

1. A custom thyristor digital modeling method considering reverse turn-off characteristics, characterized in that: Includes the following steps: Step (1) Construction of the fitting parameter calculation module; Step (2) Construction of the thyristor reverse blocking recovery module: The reverse blocking recovery module outputs the reverse recovery current in real time. It activates when the current flowing through the thyristor model in the power system digital simulation software decreases to zero, and the thyristor enters the reverse recovery phase. The time t1 when the forward conduction current of the thyristor decreases to zero is obtained through sample-and-hold. The reverse blocking recovery module represents the thyristor's reverse recovery characteristic curve as an exponential function. The value of the key parameter time constant τ in the exponential function expression is calculated using a fitting function method. Then, the time t2 when the reverse recovery current reaches its peak value is determined through relational operators and sample-and-hold. Finally, the exponential form of the reverse recovery current value is calculated in real time at different junction temperatures. The exponential function is expressed as: （1）； In equation (1), the time constant τ is （2）； The fitting function Q in equation (2) rr and I RM for （3）； （4）； In the formula, t1 is the moment when the forward conduction current of the thyristor decreases to zero, di / dt is the rate of change of the zero-crossing current corresponding to time t1, t2 is the moment when the reverse recovery current reaches its peak value, and I RM Q is the peak value of the reverse recovery current. rr To recover the charge in the reverse direction, I F The peak value of the forward current is given, τ is the time constant, and α0, α1, and α2 are the values ​​of Q. rr With di / dt, I F The fitting coefficients obtained between them, β0, β1, β2 are I RM With di / dt, I F The fitting coefficients obtained between them; Step (3) Construction of the thyristor forward blocking recovery module: The forward blocking recovery module simulates the structural composition of a thyristor's forward blocking recovery characteristics. The forward blocking recovery module obtains the minimum turn-off time t at different junction temperatures through a fitting function. q Its function is as follows: when a forward voltage is detected on the thyristor during the minimum turn-off time (i.e., before the forward blocking capability is restored), the thyristor immediately turns on; conversely, when the forward blocking capability is restored, the thyristor needs to be triggered normally to turn on. The fitted function t... q for: （5）； In the formula, t q I is the turn-off time, di / dt is the rate of change of current at the zero-crossing point, and I is the turn-off time. F For the positive current peak, λ0, λ1, and λ2 are t q With di / dt, I F The fitting coefficients obtained between them.

2. The custom thyristor digital modeling method considering reverse turn-off characteristics according to claim 1, characterized in that: The fitting parameter calculation module in step (1) is divided into two parts. One part is to calculate the rate of change of the electrical quantity at the zero-crossing current di / dt and the peak value of the positive current I. F The other part involves calculating the fitting coefficients of the fitting functions in the reverse recovery blocking module and the forward recovery blocking module at different junction temperatures.

Images