Grid-connected converter dynamic current limiting method and system for overload capacity improvement

Abstract

The application discloses a kind of grid-connected converter dynamic current limiting methods and systems for overload capacity improvement, first, according to the current rate of change when power device opens, the junction temperature of each power device in grid-connected converter is estimated in real time;Second, according to the estimated junction temperature of power device, switching frequency, DC bus voltage and the maximum junction temperature that power device can bear, the failure current of power device is predicted in real time;Third, according to the predicted current of power device failure, the output current limiting value of grid-connected converter is determined and a certain margin is retained, and current limiting value is constantly dynamically updated;Finally, based on the estimated junction temperature of power device, the rate of change of output current limiting value and the maximum junction temperature that power device can bear are carried out real-time heat dissipation control.The application can effectively improve the fault support capability of grid-connected converter and reduce its manufacturing cost under the condition of ensuring the safety of power device during power grid failure.

Description

Technical Field

[0001] This invention relates to the field of control of grid-connected converters for power electronic devices, and more particularly to a dynamic current limiting method and system for improving the overload capacity of grid-connected converters under grid fault conditions. Background Technology

[0002] With the increasing proportion of new energy generators in the power grid, the widespread application of power electronic grid-connected converters has brought new challenges to grid stability. Especially in the event of grid faults, the insufficient support capacity of the grid-connected converters can severely impact grid recovery and stability. In grid-connected converters, power devices, as current carriers, are limited by the characteristics of semiconductor materials, resulting in a much lower overload capacity than traditional synchronous generators. When grid faults such as short circuits occur, the sudden surge in current can easily cause power devices to overheat and burn out, affecting the reliable operation of the grid-connected converter.

[0003] To improve the grid-connected converter's ability to withstand grid faults, existing solutions employ parallel connection of multiple power devices to increase overcurrent protection, which is costly. Furthermore, the control program of the grid-connected converter typically includes current limiting mechanisms to protect the power devices; that is, when the output current exceeds a fixed value, it is limited to that value. However, this current limiting mechanism reduces the grid-connected converter's ability to withstand grid faults, and its control strategies and protection mechanisms may cause them to quickly disconnect from the grid during faults, further reducing their support capability. This behavior is particularly pronounced in power systems with a high proportion of renewable energy connected to the grid, potentially leading to insufficient active or reactive power support after a fault, prolonging grid recovery time, and even causing stability issues. Especially when the grid experiences voltage drops or frequency deviations, insufficient support capability of the grid-connected converter may lead to larger-scale voltage and frequency fluctuations, further exacerbating power system instability.

[0004] The method of improving the overload capacity of grid-connected converters by parallel expansion of power devices is not only costly, but also unable to meet the fault support requirements of large-scale renewable energy grid connection scenarios. Therefore, there is an urgent need to propose a dynamic current limiting method for grid-connected converters that does not require parallel expansion of power devices and is geared towards improving overload capacity. Summary of the Invention

[0005] The technical problem to be solved by this invention is: addressing the issues that existing methods for improving the overload capacity of grid-connected converters based on parallel expansion of power devices are costly and cannot meet the requirements for fault support capabilities in large-scale new energy grid-connected scenarios. This invention proposes a dynamic current limiting method and system for grid-connected converters that does not require parallel expansion of power devices and is geared towards improving overload capacity.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention proposes a dynamic current limiting method for grid-connected converters aimed at improving overload capacity, comprising the following steps:

[0008] S1. Based on the dynamic temperature-sensitive electrical parameters of the power devices during turn-on, the junction temperature T of each power device in the grid-connected converter is... j Perform real-time estimation;

[0009] S2, based on the estimated junction temperature T of the power device j and DC bus voltage U dc Switching frequency f sw and the maximum junction temperature T that power devices can withstand jm Real-time prediction of the current i when power devices fail f ;

[0010] S3. Based on the predicted current i when the power device fails. f Determine the output current limiting value i of the grid-connected converter. p It also retains a certain margin and continuously updates the current limit value dynamically;

[0011] S4, Based on the estimated junction temperature T of the power device j The rate of change of the output current limit value, di p / dt and the maximum junction temperature T that the power device can withstand jm Perform real-time intelligent heat dissipation control.

[0012] Furthermore, the dynamic current limiting method for grid-connected converters proposed in this invention, aimed at improving overload capacity, involves setting the junction temperature T of the power devices in the grid-connected converter in step S1. j The method for real-time estimation is as follows:

[0013] S101. When the grid-connected converter is offline, measure the rate of change of drain current di when the power device is turned on. D / dt, and determine the junction temperature T based on its functional relationship with the junction temperature. j ;

[0014] S102. Measure the temperature T of the heat sink by using a thermocouple installed on the power device heat sink. d ;

[0015] S103, based on the radiator temperature T d and junction temperature T j Based on the mapping relationship, establish a dataset;

[0016] S104. Change the DC bus voltage and repeat the above process to create multiple datasets.

[0017] S105. Based on the datasets obtained in S103 and S104, fit the radiator temperature T under different DC bus voltage conditions. d and junction temperature T j Functional expressions between;

[0018] S106. When the grid-connected converter is online, the measured radiator temperature T is used as the reference. d And the inverse estimation of junction temperature T obtained from the fitted expression in S105 j .

[0019] Furthermore, the dynamic current limiting method for grid-connected converters proposed in this invention for improving overload capacity includes, in S2, the estimated junction temperature T of the power device... j DC bus voltage U dc Switching frequency f sw and the maximum junction temperature T that power devices can withstand jm Real-time prediction of the current i when power devices fail f The specific method is as follows:

[0020] S201, Calculate the power device loss P loss The real-time value, which is determined by the switching loss P sw and conduction loss P on It consists of two parts, and the expression is as follows:

[0021]

[0022] Among them, E onj E represents the turn-on energy loss during the j-th switching cycle. offj Let u be the turn-off energy loss during the j-th switching cycle. DSonj Let i be the drain-source voltage when the power device is turned on during the j-th switching cycle. Dj The drain current of the power device in the j-th switching cycle is given. All of the above parameters are pre-built into a database based on the values ​​in the datasheet for future reference.

[0023] S202, Calculate the heat power P conducted to the radiator fins. th Specifically:

[0024] Assuming the heat generated by the power device is transferred uniformly in a certain direction, then for a thermal resistance of R... th The heat capacity is C th A medium of thickness d, with thermal power P A The heat power P conducted from interface A to interface B B The expression is as follows:

[0025]

[0026] The temperature relationship at the medium interface is expressed as follows:

[0027]

[0028] Where ρ is the density of the medium, and c th k is the specific heat capacity of the medium. th Let T be the thermal conductivity of the medium, and T be the temperature of the medium surface.

[0029] Establish a thermal model for the power device with five dielectric layers from the inside out. The five dielectric layers, from the inside out, include the package, silicone grease, insulating ceramic sheet, silicone grease again, and heat sink. Calculate the thermal power P of the power device. loss The heat power P conducted to the radiator fins th ;

[0030] When the heat power P is conducted to the radiator fins th <Heat dissipation power P of the radiator d At this time, the junction temperature of the power device will continuously decrease; when the heat power P conducted to the heat sink fins... th >Heat dissipation power P of the radiator d At this time, the junction temperature of the power device will continuously rise; according to the current drain current i D (k), predicting the drain current i in the next cycle. D (k+1), calculate the loss P of the power device in the next cycle. loss and thermal power P th If the heat power P th Greater than the heat dissipation power P d Then the drain current i in the next cycle will be... D (k+1) represents the predicted current i when the power device fails. f ;

[0031] Predict the drain current i in the next cycle D The expression for (k+1) is as follows:

[0032] i D (k+1)=a 11 i D (k)+a 12 u f (k)+b u1 u o (k)+b i1 i L (k),

[0033] Among them, a 11 a 12 b u1 and b i1 For parameters related to the grid-connected converter structure, u f The voltage across the filter capacitor, uo i is the output voltage of the bridge arm of the grid-connected converter. L This is the load current;

[0034] For varying junction temperatures T of power devices j and radiator temperature T d The above calculation process is performed in real time, continuously updating the current i when the power device fails. f The predicted value is used to dynamically limit the output current of the grid-connected converter.

[0035] Furthermore, the dynamic current limiting method for grid-connected converters proposed in this invention for improving overload capacity, specifically involves continuously and dynamically updating the current limiting value in step S3 as follows:

[0036] Dynamically update the output current limit value i of the grid-connected converter p The d-axis and q-axis components are used as the reference values ​​for the controller's d-axis and q-axis current outputs, respectively, with a current limiting value i. p A certain margin is allowed, the value of which is the power device failure current i. f m times, where m∈(0,1), its expression is as follows:

[0037]

[0038] Among them, i pd is i p The d-axis component, i pq is i p The q-axis component, output current limiting value i p Once determined, the values ​​of its d-axis and q-axis components are determined in real time by the commanded active power and reactive power.

[0039] Furthermore, in the dynamic current limiting method for grid-connected converters proposed in this invention to improve overload capacity, step S4 is based on the estimated junction temperature T of the power device. j The rate of change of the output current limit value, di p / dt and the maximum junction temperature T that the power device can withstand jm The principles for real-time intelligent heat dissipation control are as follows:

[0040] The air outlet of the axial fan is installed perpendicular to the radiator fins, and the power supply voltage of the axial fan is kept constant at U. m The speed of the axial fan is changed by adjusting the duty cycle D of the PWM wave input to the fan drive circuit, where D∈[0,1], thereby controlling the heat dissipation power P of the radiator. d The heat dissipation power P of the radiator d The expression is as follows:

[0041] P d =ηKAr,

[0042] Where η is the heat dissipation efficiency of the radiator, K is the motor capacity coefficient, A is the air pressure, and r is the rotational speed of the axial fan, and its expression is as follows:

[0043]

[0044] Among them, C e C is the electromotive force constant of the axial flow fan. T Φ is the torque constant of the axial flow fan. N For air gap flux, R a T is the armature resistance. m For mechanical torque;

[0045] The expression for the duty cycle D of the input PWM wave in the axial flow fan drive circuit is as follows:

[0046]

[0047] Where w1 and w2 are T j and di p The weighting factor of / dt, min(F,1) is the minimum value of F and 1.

[0048] This invention also proposes a dynamic current limiting system for grid-connected converters aimed at improving overload capacity, comprising:

[0049] The converter power device junction temperature estimation unit is used to estimate the junction temperature T of each power device in the grid-connected converter based on the dynamic temperature-sensitive electrical parameters of the power devices during turn-on. j Perform real-time estimation;

[0050] A converter power device failure current prediction unit is used to predict the failure current of the power device based on the estimated junction temperature T. j and DC bus voltage U dc Switching frequency f sw and the maximum junction temperature T that power devices can withstand jm Real-time prediction of the current i when power devices fail f ;

[0051] The converter output current limiting calculation unit is used to calculate the current i when the power device fails, based on the predicted current i. f Determine the output current limiting value i of the grid-connected converter. p It also retains a certain margin and continuously updates the current limit value dynamically;

[0052] The converter's intelligent thermal control unit is based on the estimated junction temperature T of the power devices. j The rate of change of the output current limit value, di p / dt and the maximum junction temperature T that the power device can withstand jmPerform real-time intelligent heat dissipation control.

[0053] The present invention also proposes an electronic system comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the method described in the present invention.

[0054] Finally, the present invention provides a computer-readable storage medium storing computer instructions for causing the computer to perform the method described in the present invention.

[0055] The present invention adopts the above technical solution and has the following technical effects:

[0056] This invention estimates the junction temperature of power devices to predict the current when power devices fail in real time. After retaining a certain margin, it dynamically updates the limit value of the output current of the grid-connected converter based on the predicted value of the power device failure current. Finally, it performs intelligent heat dissipation control on the power devices. This invention can effectively improve the fault support capability of the grid-connected converter and reduce its manufacturing cost while ensuring the safety of power devices during grid faults. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0058] Figure 1 These are schematic diagrams of traditional fixed-value current limiting and dynamic current limiting proposed in this invention.

[0059] Figure 2 This is the circuit equivalent schematic for calculating the drain current during the turn-on phase.

[0060] Figure 3 This is a schematic diagram showing the relationship between the rate of change of drain current and junction temperature during turn-on.

[0061] Figure 4 This is the topology diagram of a grid-connected converter.

[0062] Figure 5 This is a flowchart of the method of the present invention. Detailed Implementation

[0063] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0064] To achieve the above objectives, this invention proposes a dynamic current limiting method for grid-connected converters aimed at improving overload capacity. A schematic diagram of the dynamic current limiting method is shown below. Figure 1 As shown, (a) is a schematic diagram of traditional fixed-value current limiting, and (b) is a schematic diagram of dynamic current limiting proposed in this invention. The method flow of this invention is referenced below. Figure 5 As shown, the specific steps include:

[0065] S1. Based on the dynamic temperature-sensitive electrical parameters of the power devices during turn-on, the junction temperature T of each power device in the grid-connected converter is... j The specific steps for real-time estimation are as follows:

[0066] (1) When the grid-connected converter is offline, measure the rate of change of drain current di when the power device is turned on. D / dt, and determine the junction temperature T based on its functional relationship with the junction temperature. j .

[0067] The equivalent circuit diagram for calculating the drain current during the turn-on phase is shown below. Figure 2 As shown, considering the channel length modulation effect of power devices, the expression for the drain current is as follows:

[0068]

[0069] Where W is the width of the conductive channel of the power device, L is the length of the conductive channel of the power device, λ is the modulation parameter for the length of the conductive channel of the power device, μ0 is the effective electron mobility within the conductive channel of the power device, and C ox For gate oxide capacitance, u thres u is the threshold voltage of the power device. GS U is the gate-source voltage. dc This is the DC bus voltage.

[0070] Differentiating both sides of the above equation with respect to time t, we get the rate of change of drain current di when the power device is turned on. D The expression for / dt is as follows:

[0071]

[0072] When the DC bus voltage remains constant, the rate of change of drain current di when the power device is turned on is... D / dt and junction temperature T j To approximate a linear relationship, the function expression is as follows:

[0073]

[0074] Wherein, gate-source voltage u GS U is a constant GSk0 and k1 are coefficients that can be measured experimentally. The rate of change of drain current di when the power device is turned on is... D / dt and junction temperature T j Relationship diagram as follows Figure 3 As shown.

[0075] (2) Measure the temperature T of the heat sink by using a thermocouple installed on the heat sink of the power device. d .

[0076] Thermocouples should be placed as close as possible to power devices to accurately measure the resulting heatsink temperature rise.

[0077] (3) Based on the radiator temperature T d and junction temperature T j Establish the mapping relationship and build the dataset.

[0078] (4) Change the DC bus voltage and repeat the above process to establish multiple datasets.

[0079] (5) Based on the datasets obtained in (3) and (4), fit the radiator temperature T under different DC bus voltage conditions. d and junction temperature T j Functional expressions between.

[0080] For the function T to be fitted j (T d Define the residual function S(T) j (T d ))as follows:

[0081]

[0082] Among them, T di Let T be the i-th data point of the radiator temperature in the dataset. ji Let be the i-th data point of the junction temperature of the power device in the dataset, n be the total number of data points in the dataset, ε be the tolerance limit, and max(0,|T j (T di )-T ji |-ε) is 0 and |T j (T di )-T ji The maximum value between |-ε. To obtain the best fitting function, the residual function should be minimized.

[0083] The fitting function is usually obtained by transforming a linear function into a nonlinear function. First, we define a linear regression model as follows:

[0084] T j (T d )=ω T θ(T d)+b;

[0085] Where ω is the model's weight vector, ω T It is its transpose vector, b is the bias term, θ(T) d ) is the input feature quantity T d Through the kernel function K(T) d ,T j Nonlinear mapping of ).

[0086] To handle nonlinear problems, the kernel function can convert the input feature quantity T d Mapping to a higher-dimensional feature space simplifies computation by enabling linear regression models in that space. The kernel function used is K(T). d ,T j The expression for ) is as follows:

[0087]

[0088] Among them, T j For a given data point representing the junction temperature of a power device in the dataset, σ is the width parameter of the kernel function, which determines the smoothness of the kernel function. It controls the degree to which the similarity between samples decreases as distance increases. When σ is large, it indicates that the similarity decays slowly, meaning that even if two samples are far apart, they will still have a high similarity. When σ is small, it indicates that the similarity decays quickly, meaning that only very close samples will be considered similar.

[0089] To minimize the residual function and limit the model complexity, the specific objective function is defined as follows:

[0090]

[0091] Where, ||ω|| 2 It is a regularization term for model complexity, aiming to minimize the sum of squared weights and prevent overfitting; ξ i ε is the relaxation factor of the i-th variable in the dataset, indicating whether the i-th training point has crossed the ε boundary; C is the regularization parameter, controlling the model's tolerance to training error. A larger C value allows for smaller errors but may lead to overfitting, while a smaller C value encourages a smoother model. The optimization goal is to minimize the weighted sum of model complexity and error.

[0092] Finally, the specific fitting decision function is as follows:

[0093]

[0094] Where, α i These are Lagrange multipliers used to control the contribution of support vectors to the regression model.

[0095] When the grid-connected converter is offline, the parameters ω, b, and α under different DC bus voltages are obtained by training the objective function using the dataset and optimizing it. i To determine the expression of the fitting function.

[0096] (6) When the grid-connected converter is online, the measured radiator temperature T d The corresponding decision function T is called based on the DC bus voltage. j (T d This allows you to estimate the junction temperature of power devices.

[0097] S2, based on the estimated junction temperature T of the power device j DC bus voltage U dc Switching frequency f sw and the maximum junction temperature T that power devices can withstand jm Real-time prediction of the current i when power devices fail f The specific method is as follows:

[0098] (1) Calculate the power device loss P loss The real-time value, which is determined by the switching loss P sw and conduction loss P on It consists of two parts, and the expression is as follows:

[0099]

[0100] Among them, E onj E represents the turn-on energy loss during the j-th switching cycle. offj Let u be the turn-off energy loss during the j-th switching cycle. DSonj Let i be the drain-source voltage when the power device is turned on during the j-th switching cycle. Dj Let be the drain current of the power device in the j-th switching cycle. All the above parameters are pre-databaseed based on values ​​from the datasheet for future reference.

[0101] (2) Calculate the heat power P conducted to the radiator fins. th

[0102] Assuming the heat generated by the power device is uniformly transferred along the x-direction, for a thin sheet of thickness d, the heat power at points x and x+Δx is analyzed, and the expression of the heat balance equation is as follows:

[0103] (P x -P x+Δx )Δt=ρSΔxc th ΔT;

[0104] Among them, P x Let P be the heat power at point x. x+Δx Let be the heat power at x+Δx, ρ be the density of the medium, S be the area of ​​the thin sheet, and c be the heat power at x+Δx.th Let ΔT be the specific heat capacity of the medium, and ΔT be the temperature difference between the two surfaces of the medium.

[0105] When Δx→0 and Δt→0, the expression is as follows:

[0106]

[0107] The expression for Fourier's heat conduction formula is as follows:

[0108]

[0109] Where, k th denoted as , where is the thermal conductivity of the medium.

[0110] Substituting into the Fourier heat conduction formula, we obtain the following expression:

[0111]

[0112] Since the thickness d of the thin sheet is very small, the left side of the above equation can be approximated as:

[0113]

[0114] Therefore, we can obtain:

[0115]

[0116] Wherein, the thermal resistance R of the medium th =d / k th S, heat capacity C th =ρc th dS.

[0117] For a medium of thickness d, the thermal power P A The heat power P conducted from interface A to interface B B The expression is as follows:

[0118]

[0119] Power devices pass through five dielectric layers from the internal semiconductor to the air: encapsulation, silicone grease, insulating ceramic sheet, silicone grease again, and heat sink. By establishing thermal models for each of these layers using the methods described above, the thermal power P of the power device can be calculated. loss The heat power P conducted to the radiator fins th .

[0120] When the heat power P is conducted to the radiator fins th <Heat dissipation power P of the radiator d At this time, the junction temperature of the power device will continuously decrease; when the heat power P conducted to the heat sink fins... th >Heat dissipation power P of the radiatord At this time, the junction temperature of the power device will continuously rise. Based on the current drain current i... D (k), predicting the drain current i in the next cycle. D (k+1), calculate the loss P of the power device in the next cycle. loss and thermal power P th If the heat power P th Greater than the heat dissipation power P d Then the drain current i in the next cycle will be... D (k+1) represents the predicted current i when the power device fails. f .

[0121] Predict the drain current i in the next cycle D The expression for (k+1) is as follows:

[0122] i D (k+1)=a 11 i D (k)+a 12 u f (k)+b u1 u o (k)+b i1 u g (k);

[0123] Among them, a 11 a 12 b u1 and b i1 For parameters related to the grid-connected converter structure, u f The voltage across the filter capacitor, u o For the output voltage of the grid-connected converter bridge arm, u g This is the grid voltage. The topology of the grid-connected converter is as follows: Figure 4 As shown.

[0124] Requires a 11 a 12 b u1 and b i1 First, the state-space model of the grid-connected converter is established, and its expression is as follows:

[0125]

[0126] Wherein, the state variable x(k) = [i D (k)u f (k)i L (k)] T i L For filter inductor L f The current on it.

[0127] For varying junction temperatures T of power devicesj and radiator temperature T d The above calculation process is performed in real time, continuously updating the current i when the power device fails. f The predicted value is used to dynamically limit the output current of the grid-connected converter.

[0128] S3. Based on the predicted current i when the power device fails. f Determine the output current limiting value i of the grid-connected converter. p The specific steps for maintaining a certain margin and continuously and dynamically updating the current limit value are as follows:

[0129] Dynamically update the output current limit value i of the grid-connected converter p The d-axis and q-axis components are used as reference values ​​for the controller's d-axis and q-axis current outputs, respectively. Current limiting value i p A certain margin is allowed, the value of which is the power device failure current i. f The expression for m times (m∈(0,1)) is as follows:

[0130]

[0131] Among them, i pd is i p The d-axis component, i pq is i p The q-axis component. Output current limiting value i p Once determined, the values ​​of its d-axis and q-axis components are determined in real time by the commanded active power and reactive power.

[0132] S4, Based on the estimated junction temperature T of the power device j The rate of change of the output current limit value, di p / dt and the maximum junction temperature T that the power device can withstand jm The method for real-time intelligent heat dissipation control is as follows:

[0133] (1) Install the air outlet of the axial flow fan perpendicular to the radiator fins, and keep the power supply voltage of the axial flow fan constant at U. m The speed of the axial fan is changed by adjusting the duty cycle D (D∈[0,1]) of the PWM wave input to the fan drive circuit, thereby controlling the heat dissipation power P of the radiator. d The heat dissipation power P of the radiator d The expression is as follows:

[0134] P d =ηKAr

[0135] Where η is the heat dissipation efficiency of the radiator, K is the motor capacity coefficient, A is the air pressure, and r is the rotational speed of the axial fan, and its expression is as follows:

[0136]

[0137] Among them, C e C is the electromotive force constant of the axial flow fan. T Φ is the torque constant of the axial flow fan. N For air gap flux, R a T is the armature resistance. m This refers to mechanical torque.

[0138] (2) In order to determine the duty cycle D of the input PWM wave of the axial fan drive circuit and achieve the best heat dissipation effect, the expression for the duty cycle D is as follows:

[0139]

[0140] Where w1 and w2 are T j and di p The weighting factors of / dt (all greater than 0), w1 represents when di p When / dt remains constant, T j For each additional unit, the change in D; w2 represents the change in T when T... j When it remains unchanged, di p For each unit increase in / dt, the change in D is represented by min(F,1), which is the minimum of F and 1.

[0141] The weighting factors w1 and w2 are estimated using the least squares method. The optimal weighting factors w1 and w2 are obtained by minimizing the sum of squares of the error terms. The objective of the least squares method is to minimize the following objective function:

[0142]

[0143] The w1 and w2 corresponding to the minimum value of the above formula are the expected values.

[0144] Example 2:

[0145] This embodiment proposes a dynamic current limiting system for grid-connected converters aimed at improving overload capacity, including:

[0146] The converter power device junction temperature estimation unit is used to estimate the junction temperature T of each power device in the grid-connected converter based on the dynamic temperature-sensitive electrical parameters of the power devices during turn-on. j Perform real-time estimation;

[0147] A converter power device failure current prediction unit is used to predict the failure current of the power device based on the estimated junction temperature T. j and DC bus voltage U dc Switching frequency f sw and the maximum junction temperature T that power devices can withstand jmReal-time prediction of the current i when power devices fail f ;

[0148] The converter output current limiting calculation unit is used to calculate the current i when the power device fails, based on the predicted current i. f Determine the output current limiting value i of the grid-connected converter. p It also retains a certain margin and continuously updates the current limit value dynamically;

[0149] The converter's intelligent thermal control unit is based on the estimated junction temperature T of the power devices. j The rate of change of the output current limit value, di p / dt and the maximum junction temperature T that the power device can withstand jm Perform real-time intelligent heat dissipation control.

[0150] The specific implementation details of each of the above units correspond one-to-one with the steps of the method proposed in Embodiment 1 of the present invention, and will not be repeated here.

[0151] Example 3:

[0152] This embodiment proposes a computer-readable storage medium storing a computer program thereon. When the computer program is executed by a processor, it implements the steps of the method described in this invention, which will not be repeated here.

[0153] Example 4:

[0154] This embodiment also proposes an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor.

[0155] It should be noted that the processing flows of Embodiments 2 to 4 correspond to the specific steps of the method provided in the embodiments of the present invention, and have the corresponding functional modules and beneficial effects of the method. Technical details not described in detail in this embodiment can be found in the method provided in the embodiments of the present invention.

[0156] The program code used to implement the methods of this application may be written in any combination of one or more programming languages. This program code may be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the functions / operations specified in the flowcharts and / or block diagrams are implemented. The program code may be executed entirely on a machine, partially on a machine, as a standalone software package partially on a machine and partially on a remote machine, or entirely on a remote machine or server.

[0157] In the context of this application, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media can be, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0158] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0159] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A dynamic current limiting method for grid-connected converters aimed at improving overload capacity, characterized in that, Includes the following steps: S1. Based on the dynamic temperature-sensitive electrical parameters of the power devices during turn-on, the junction temperature T of each power device in the grid-connected converter is... j Perform real-time estimation; S2, based on the estimated junction temperature T of the power device j and DC bus voltage U dc Switching frequency f sw and the maximum junction temperature T that power devices can withstand jm Real-time prediction of the current i when power devices fail f ; S3. Based on the predicted current i when the power device fails. f Determine the output current limiting value i of the grid-connected converter. p It also retains a certain margin and continuously updates the current limit value dynamically; S4, Based on the estimated junction temperature T of the power device j The rate of change of the output current limit value di p / dt and the maximum junction temperature T that the power device can withstand jm Perform real-time intelligent heat dissipation control.

2. The dynamic current limiting method for grid-connected converters aimed at improving overload capacity as described in claim 1, characterized in that, S1 specifies the junction temperature T of the power devices in the grid-connected converter. j The method for real-time estimation is as follows: S101. When the grid-connected converter is offline, measure the rate of change of drain current di when the power device is turned on. D / dt, and determine the junction temperature T based on its functional relationship with the junction temperature. j ; S102. Measure the temperature T of the heat sink by using a thermocouple installed on the power device heat sink. d ; S103, based on the radiator temperature T d and junction temperature T j Based on the mapping relationship, establish a dataset; S104. Change the DC bus voltage and repeat the above process to create multiple datasets. S105. Based on the datasets obtained in S103 and S104, fit the radiator temperature T under different DC bus voltage conditions. d and junction temperature T j Functional expressions between; S106. When the grid-connected converter is online, the measured radiator temperature T is used as the reference. d And the inverse estimation of junction temperature T obtained from the fitted expression in S105 j .

3. The dynamic current limiting method for grid-connected converters aimed at improving overload capacity as described in claim 2, characterized in that, When the DC bus voltage remains constant, the rate of change of drain current di when the power device is turned on is... D / dt and junction temperature T j To approximate a linear relationship, the function expression is as follows: Wherein, gate-source voltage u GS U is a constant GS k0 and k1 are coefficients, obtained through experiments; The rate of change of drain current di when the power device is turned on D The expression for / dt is as follows: Where W is the width of the conductive channel of the power device, L is the length of the conductive channel of the power device, λ is the modulation parameter for the length of the conductive channel of the power device, μ0 is the effective electron mobility within the conductive channel of the power device, and C ox For gate oxide capacitance, u thres U is the threshold voltage of the power device. dc This is the DC bus voltage.

4. The dynamic current limiting method for grid-connected converters aimed at improving overload capacity as described in claim 2, characterized in that, Determine the radiator temperature T when the DC bus voltage remains constant. d and junction temperature T j The method for fitting expressions between them is as follows: The fitted function T is obtained by training with the dataset. j (T d The expression for ) when the residual function S(T) j (T d The optimal fit is achieved when the minimum value is reached. T j and T d The expression for the fitting function between them is as follows: Where, α i These are Lagrange multipliers, where n is the total number of data points in the dataset, and T is the number of data points in the dataset. d For the data points of radiator temperature in the dataset, T j For the data points of junction temperature of power devices in the dataset, K(T) d ,T j ) is the kernel function, and b is the bias term of the linear regression model; Kernel function used K(T) d ,T j The expression for ) is as follows: Where σ is the width parameter of the kernel function; The expression for the linear regression model used is as follows: T j (T d )=ω T θ(T d )+b, Where ω is the model's weight vector, ω T It is its transpose vector, θ(T) d ) is the input feature quantity T d Through the kernel function K(T) d ,T j Nonlinear mappings; The residual function used S(T) j (T d The expression for )) is as follows: Among them, T di Let T be the i-th data point of the radiator temperature in the dataset. ji Let be the i-th data point of the junction temperature of the power device in the dataset, ε be the allowable error limit, and max(0,|T) j (T di )-T ji |-ε) is 0 and |T j (T di )-T ji The maximum value between |-ε; with the goal of minimizing the residual function and limiting the complexity of the model, the specific objective function is defined as follows: Where, ||ω|| 2 It is the regularization term for model complexity, ξ i is the relaxation factor of the i-th variable in the dataset, C is the regularization parameter, and the optimization objective is to minimize the weighted sum of the model's complexity and error.

5. A dynamic current limiting method for grid-connected converters aimed at improving overload capacity as described in claim 1, characterized in that, S2 is based on the estimated junction temperature T of the power device. j DC bus voltage U dc Switching frequency f sw and the maximum junction temperature T that power devices can withstand jm Real-time prediction of the current i when power devices fail f The specific method is as follows: S201, Calculate the power device loss P loss The real-time value, which is determined by the switching loss P sw and conduction loss P on It consists of two parts, and the expression is as follows: Among them, E onj E represents the turn-on energy loss during the j-th switching cycle. offj For the turn-off energy loss in the j-th switching cycle, u DSonj Let i be the drain-source voltage when the power device is turned on during the j-th switching cycle. Dj The drain current of the power device in the j-th switching cycle is given. All of the above parameters are pre-built into a database based on the values ​​in the datasheet for future reference. S202, Calculate the heat power P conducted to the radiator fins. th Specifically: Assuming the heat generated by the power device is transferred uniformly in a certain direction, then for a thermal resistance of R... th The heat capacity is C th A medium of thickness d, with thermal power P A The heat power P conducted from interface A to interface B B The expression is as follows: The temperature relationship at the medium interface is expressed as follows: Where ρ is the density of the medium, and c th k is the specific heat capacity of the medium. th Let T be the thermal conductivity of the medium, and T be the temperature of the medium surface. Establish a thermal model for the power device with five dielectric layers from the inside out. The five dielectric layers, from the inside out, include the package, silicone grease, insulating ceramic sheet, silicone grease again, and heat sink. Calculate the thermal power P of the power device. loss The heat power P conducted to the radiator fins th ; When the heat power P is conducted to the radiator fins th <Heat dissipation power P of the radiator d At this time, the junction temperature of the power device will continuously decrease; when the heat power P conducted to the heat sink fins... th >Heat dissipation power P of the radiator d At this time, the junction temperature of the power device will continue to rise; according to the current drain current i D (k), predicting the drain current i in the next cycle. D (k+1), calculate the loss P of the power device in the next cycle. loss and thermal power P th If the heat power P th Greater than the heat dissipation power P d Then the drain current i in the next cycle will be... D (k+1) represents the predicted current i when the power device fails. f ; Predict the drain current i in the next cycle D The expression for (k+1) is as follows: i D (k+1)=a 11 i D (k)+a 12 u f (k)+b u1 u o (k)+b i1 i L (k), Among them, a 11 a 12 b u1 and b i1 For parameters related to the grid-connected converter structure, u f The voltage across the filter capacitor, u o i is the output voltage of the bridge arm of the grid-connected converter. L This is the load current; For varying junction temperatures T of power devices j and radiator temperature T d The above calculation process is performed in real time, continuously updating the current i when the power device fails. f The predicted value is used to dynamically limit the output current of the grid-connected converter.

6. The dynamic current limiting method for grid-connected converters aimed at improving overload capacity as described in claim 1, characterized in that, The current limit value is continuously and dynamically updated in S3 as follows: Dynamically update the output current limit value i of the grid-connected converter p The d-axis and q-axis components are used as the reference values ​​for the controller's d-axis and q-axis current outputs, respectively, with a current limiting value i. p A certain margin is allowed, the value of which is the power device failure current i. f m times, where m∈(0,1), its expression is as follows: Among them, i pd is i p The d-axis component, i pq is i p The q-axis component, output current limiting value i p Once determined, the values ​​of its d-axis and q-axis components are determined in real time by the commanded active power and reactive power.

7. A dynamic current limiting method for grid-connected converters aimed at improving overload capacity as described in claim 1, characterized in that, S4 is based on the estimated junction temperature T of the power device. j The rate of change of the output current limit value di p / dt and the maximum junction temperature T that the power device can withstand jm The principles for real-time intelligent heat dissipation control are as follows: The air outlet of the axial fan is installed perpendicular to the radiator fins, and the power supply voltage of the axial fan is kept constant at U. m The speed of the axial fan is changed by adjusting the duty cycle D of the PWM wave input to the fan drive circuit, where D∈[0,1], thereby controlling the heat dissipation power P of the radiator. d The heat dissipation power P of the radiator d The expression is as follows: P d =ηKAr, Where η is the heat dissipation efficiency of the radiator, K is the motor capacity coefficient, A is the air pressure, and r is the rotational speed of the axial fan, and its expression is as follows: Among them, C e C is the electromotive force constant of the axial flow fan. T Φ is the torque constant of the axial flow fan. N For air gap flux, R a T is the armature resistance. m For mechanical torque; The expression for the duty cycle D of the input PWM wave in the axial flow fan drive circuit is as follows: Where w1 and w2 are T j and di p The weighting factor of / dt, min(F,1) is the minimum value of F and 1.

8. A dynamic current limiting system for grid-connected converters aimed at improving overload capacity, characterized in that, include: The converter power device junction temperature estimation unit is used to estimate the junction temperature T of each power device in the grid-connected converter based on the dynamic temperature-sensitive electrical parameters of the power devices during turn-on. j Perform real-time estimation; A converter power device failure current prediction unit is used to predict the failure current of the power device based on the estimated junction temperature T. j and DC bus voltage U dc Switching frequency f sw and the maximum junction temperature T that power devices can withstand jm Real-time prediction of the current i when power devices fail f ; The converter output current limiting calculation unit is used to calculate the current i when the power device fails, based on the predicted current i. f Determine the output current limiting value i of the grid-connected converter. p It also retains a certain margin and continuously updates the current limit value dynamically; The converter's intelligent thermal control unit is based on the estimated junction temperature T of the power devices. j The rate of change of the output current limit value di p / dt and the maximum junction temperature T that the power device can withstand jm Perform real-time intelligent heat dissipation control.

9. An electronic system comprising: At least one processor; And a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, characterized in that the instructions are executed by the at least one processor to enable the at least one processor to perform the method according to any one of claims 1-8.

10. A computer-readable storage medium storing computer instructions, characterized in that, The computer instructions are used to cause the computer to perform the method according to any one of claims 1-8.

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