DC / DC converter reliability evaluation method and related device

Abstract

The invention discloses a DC / DC converter reliability evaluation method and a related device, and the method comprises the steps: constructing an electrothermal coupling model of a power switch module of a Boost full-bridge boost isolation converter BFBIC combined DC / DC converter topological structure, and obtaining the power loss and junction temperature change conditions; constructing a life prediction model based on the junction temperature change condition, and calculating a failure rate in combination with a fatigue damage accumulation model; and establishing a calculation model of the outage probability of the series / parallel module based on the fault rate, and evaluating the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter by using an improved reliability block diagram method. The method provided by the invention is helpful for reducing the evaluation error of the equipment reliability, and can provide data support for the construction and development of a novel power system.

Description

Technical Field

[0001] The invention belongs to the technical field of DC / DC converter reliability assessment, and in particular relates to a DC / DC converter reliability assessment method and related devices. Background Art

[0002] Wind power all-DC power generation system can effectively overcome the problems of harmonic resonance and reactive power transmission in traditional AC wind power system, and has broad development prospects. As the key equipment of wind power all-DC power generation system, the reliability of DC / DC converter is crucial to the safe and stable operation of the whole system.

[0003] At present, most DC / DC converters use Boost full-bridge isolation converters as modules, and connect multiple modules in parallel before and in series to meet the requirements of high power and high transformation ratio. However, as an important component of the Boost full-bridge isolation converter module, the power switch module is easily affected by factors such as the surrounding environment, operating conditions, and device aging during actual operation, leading to its failure. In addition, according to statistics on the reliability of power electronic equipment, equipment failures caused by the failure of the power switch module alone account for about 34%. Therefore, evaluating the reliability of the power switch module is of great significance to the research on the reliability of DC / DC converters. There is a technology that models and analyzes the reliability of the converter valve module and its secondary sub-modules of the flexible DC transmission converter; there is a technology that quantitatively calculates the reliability of the converter valve model when using different types of thyristors; there is a technology that establishes a modular multilevel converter reliability model based on the topological analysis of the modular multilevel converter. Although the above technologies evaluate the reliability of the device, the reliability of its module is mostly obtained through the device reliability evaluation method based on the reliability manual and the device evaluation method based on the failure mechanism. However, the data in the above two technologies are usually based on product samples or specific test conditions provided by the manufacturer. Not only do they lack representativeness and cannot fully reflect the operating conditions, but the data updates are delayed and cannot accurately reflect the reliability of the latest devices, resulting in large errors in the evaluation results. Summary of the invention

[0004] The purpose of the present invention is to provide a DC / DC converter reliability assessment method and related devices to solve the problem that the traditional DC / DC converter reliability assessment method cannot be fully applied to the reliability assessment of the Boost full-bridge boost isolation converter combined DC / DC converter in the wind farm DC collection system.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a DC / DC converter reliability assessment method, comprising:

[0007] Construct an electro-thermal coupling model of the power switch module of the Boost full-bridge boost isolation converter BFBIC combined DC / DC converter topology to obtain the power loss and junction temperature changes;

[0008] Build a life prediction model based on junction temperature changes, and calculate the failure rate using a fatigue damage accumulation model;

[0009] A calculation model for the shutdown probability of series / parallel modules is established based on the failure rate, and the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter is evaluated using the improved reliability block diagram method.

[0010] Furthermore, an electrothermal coupling model of a power switch module of a Boost full-bridge boost isolation converter BFBIC combined DC / DC converter topology is constructed, including:

[0011] For the Boost full-bridge step-up isolation converter combined DC / DC converter, a hybrid two-stage modular integration of input parallel connection, output series connection and input parallel connection, output parallel connection is adopted.

[0012] Furthermore, the power loss and junction temperature changes are obtained, including:

[0013] Establish power loss models of IGBT module and FWD module. The power loss model of FWD module is the same as the power loss of FWD in the power loss model of IGBT module.

[0014] (1) IGBT conduction loss

[0015] P CL,I =V ce ·i c,I ·D

[0016] V ce (i c ,T I )=V ce0 (T I )+r ce (T I )i c

[0017] V ce0 (T I )=V ce，25℃ +TC V (T I -25)

[0018] r ce (T I )=r ce，25℃ +TC r (T I -25)

[0019]

[0020] Where Vce is the collector-emitter saturation voltage drop, i c,I is the collector current, D is the duty cycle; where: T I is the junction temperature; V ce0 is the initial saturation pressure drop; r ce is the on-resistance; V ce,25℃ is the saturation voltage drop of IGBT at 25°C; r ce,25℃ is the on-resistance of the IGBT at 25°C; TC V and TC r Respectively represent V ce and r ce The temperature coefficient of; D(t) is the duty cycle function (time domain); k pi The value is 0.965; k di The value is 0.00065; k pv The value is 0.003; T i The value is 0.0045; △U is the difference between the input DC voltage and the reference voltage; δ(t) is the impulse function; 1(t) is the unit step function;

[0021] (2) IGBT switching losses

[0022]

[0023] P sw,I =P on,I +P off,I

[0024] In the formula, f sw is the switching frequency, E on,I 、E off,I are the turn-on and turn-off loss energies of the IGBT, U dc 、i c,I is the operating voltage and current of IGBT, U N 、i N is the rated voltage and current, K on,I , K off,I K is the influence coefficient of IGBT gate resistance on turn-on and turn-off losses; T,I is the temperature correction coefficient of switching energy loss;

[0025] (3) IGBT total power loss P I for

[0026] P I =P CL,I +P sw,I

[0027] (4) FWD conduction loss

[0028] P CL,F =V F ·i c,F ·(1-D)=f(i c,F ,T F )·i c,F (1-D)

[0029] Where: T F is the FWD junction temperature;

[0030] (5) FWD turn-off loss

[0031]

[0032] Where: E off,F is the energy loss of FWD reverse recovery; K off,F K is the influence coefficient of FWD forward resistance on turn-off loss; T,F is the temperature coefficient of the turn-off energy loss;

[0033] (6) Total FWD loss P F for

[0034] P F =P CL,F +P sw,F

[0035] Based on the losses of IGBT modules and FWD modules, the junction temperature evaluation model of IGBT modules and FWD modules is constructed using thermoelectric analogy theory;

[0036] The Foster thermal network model is used to evaluate the junction temperature of the IGBT module and the FWD module. First, the thermal parameters are converted into electrical parameters using the thermoelectric analogy theory.

[0037] The chip-to-case R in the IGBT module is connected in the Foster thermal network. thjc It is equivalent to a fourth-order RC electrical network, the shell-heat sink R thch and radiator-ambient R thha A first-order RC electrical network is used;

[0038]

[0039] τ i =R i ·C i

[0040] T I =P I ·(Z thjc_T +Z thch_T )+(P I+P F )·Z thha +T a

[0041] T F =P F ·(Z thjc_D +Z thch_D )+(P I +P F )·Z thha +T a

[0042] T D,F =P F ·(Z 0jc_D +Z 0cs_D )+P F ·Z 0sa +T a

[0043] Where: Z is thermal impedance; n is the order of Foster equivalent thermal network model; τ i is the time constant of the i-th order Foster equivalent thermal network model; R i , C i are the equivalent thermal resistance and thermal capacitance of chip-to-shell respectively; Z thjc_T is the thermal impedance of the IGBT chip-to-case in the IGBT module; Z thch_T is the thermal impedance of the IGBT case-heat sink in the IGBT module; Z thjc_D is the thermal impedance of the FWD chip-to-shell in the IGBT module; Z thch_D is the thermal impedance of the FWD tube case-heat sink in the IGBT module; Z thta is the IGBT module heat sink-environment thermal impedance; Z 0jc_D is the FWD module chip-to-case thermal impedance; Z 0cs_D is the thermal impedance of the FWD module shell and heat sink; Z 0sa is the FWD module heat sink-environment thermal impedance; T a is the ambient temperature.

[0044] Furthermore, a life prediction model is constructed based on the change of junction temperature, including:

[0045] The rain flow algorithm is used to accurately count the number of module fluctuations at different junction temperature averages and fluctuation amplitudes within a certain period of time, and then the damage degree is calculated to complete the life assessment.

[0046] The Coffin-Manson-Arrheniu analytical model is used to predict the life of IGBT modules and FWD modules;

[0047]

[0048] Where: ΔT j Indicates the junction temperature difference, T m Represents the average junction temperature, N f Indicates the working condition ΔT j and T m The number of failure cycles under the condition of α and β are module parameters, and their values ​​are 3.025×105 and -0.5039 respectively. Ea ​​is the activation energy, and its value is 9.89×10-20J. KB is the Boltzmann constant, and its value is 1.382×10-23J / K.

[0049] Furthermore, the failure rate is calculated by combining the fatigue damage accumulation model, including:

[0050] The linear fatigue damage accumulation model is used to calculate the failure rate of the IGBT module and FWD module. The calculation formula is:

[0051]

[0052] Where: N i is the number of cycles under working condition i; X To evaluate the failure rate of type X modules.

[0053] Furthermore, a calculation model for the shutdown probability of series / parallel modules is established based on the failure rate, including:

[0054] In the series module, the calculation model of the outage probability of the module composed of N components in series is:

[0055]

[0056] Where: λseries is the failure rate of the series modules in the non-redundant mode; μseries is the repair rate of the series modules in the non-redundant mode; λ i is the failure rate of the ith series submodule; μ i is the repair rate of the ith series submodule; TMTTR,i is the repair time of the ith series submodule;

[0057] In the parallel module, the calculation model of the outage probability of the parallel module with N components is:

[0058]

[0059]

[0060] Where: parallel is the failure rate of parallel modules in non-redundant mode; μ parallel is the repair rate of the parallel module in the non-redundant mode; TMTTR,i is the repair time of the i-th parallel submodule; μ iis the repair rate of the i-th parallel submodule.

[0061] Furthermore, the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter is evaluated using the improved reliability block diagram method, including:

[0062] The Boost full-bridge boost isolation converter combined DC / DC converter is divided into four hierarchical modules, and the outage probability model of the four hierarchical modules of the DC / DC converter is constructed:

[0063] In the four-level BFBIC module, all components are connected in series; the outage probability model of the four-level BFBIC module is:

[0064]

[0065] Where: BFBIC and μ BFBIC are the failure rate and repair rate of the four-level module BFBIC module respectively; IGBT , C , T , FWD , L They are the failure rates of IGBT module, capacitor, transformer T, FWD module, and inductor respectively; T C 、T IGBT 、T T 、T FWD 、T L They are the average repair time of capacitors, IGBT modules, transformer T, FWD modules, and inductors respectively; F is the number of capacitors; U is the number of IGBT modules; Q is the number of transformers; V is the number of FWD modules; and Z is the number of inductors;

[0066] In the three-level IPOS module, multiple BFBIC modules are connected in parallel and then in series. The outage probability model of the IPOS module is:

[0067]

[0068] Where: IPOS and μ IPOS are the failure rate and repair rate of IPOS modules, respectively; θ is the number of BFBIC modules;

[0069] In the secondary module IPOP module, each IPOS module is connected in parallel to realize the high-power application of the DC / DC converter. Its outage probability model is:

[0070]

[0071] Where: IPOP and μIPOP They are the failure rate and repair rate of IPOP module respectively; is the number of IPOS modules;

[0072] In the primary module Boost full-bridge boost isolation converter combined DC / DC converter, when evaluating the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter, the influence of the hardware main circuit on the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter is considered; its outage probability model is:

[0073] λ DC / DC =λ IPOP

[0074] μ DC / DC =μ IPOP

[0075] Where: DC / DC and μ DC / DC They are the failure rate and repair rate of the primary module DC / DC converter respectively;

[0076] Assuming that the BFBIC module topology remains unchanged, the calculation formula for the Boost full-bridge boost isolation converter combined DC / DC converter topology at different voltage levels is:

[0077]

[0078] Where: θ k is the number of IPOS modules in the DC / DC converter; ω is the number of IPOP modules in the Boost full-bridge boost isolation converter combined DC / DC converter; U DC / DC P is the output voltage of the Boost full-bridge boost isolation converter combined DC / DC converter; DC / DC is the output power of the Boost full-bridge boost isolation converter combined DC / DC converter; U BFBIC is the output voltage of the BFBIC module; P BFBIC is the output power of the BFBIC module.

[0079] In a second aspect, the present invention provides a DC / DC converter reliability assessment system, comprising:

[0080] The junction temperature change output module is used to construct the electrothermal coupling model of the power switch module of the Boost full-bridge boost isolation converter BFBIC combined DC / DC converter topology structure to obtain the power loss and junction temperature change;

[0081] Failure rate calculation module, used to build a life prediction model based on junction temperature changes and calculate the failure rate in combination with the fatigue damage accumulation model;

[0082] The evaluation output module is used to establish a calculation model for the shutdown probability of series / parallel modules based on the failure rate, and to evaluate the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter using the improved reliability block diagram method.

[0083] In a third aspect, the present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of a DC / DC converter reliability assessment method when executing the computer program.

[0084] In a fourth aspect, the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of a DC / DC converter reliability assessment method are implemented.

[0085] Compared with the prior art, the present invention has the following technical effects:

[0086] The present invention proposes a DC / DC converter reliability assessment method based on the topological structure and operating conditions of the Boost full-bridge boost isolation converter combined DC / DC converter. First, the wind farm DC collection system and its key equipment are analyzed; secondly, based on the analysis of the topological structure and operating conditions of the Boost full-bridge boost isolation converter combined DC / DC converter, an electrothermal coupling model of its power switch module is constructed to analyze its power loss and junction temperature change; finally, the failure rate is calculated by combining the life prediction model and fatigue damage accumulation model of the key module, and the reliability of the DC / DC converter is assessed using the improved reliability block diagram method. While reducing the assessment error of equipment reliability, data support can be provided for the construction and development of new power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Figure 1 It is a topological structure diagram of the BFBIC module of the present invention.

[0088] Figure 2 It is a topological structure diagram of the BFBIC combined DC / DC converter of the present invention.

[0089] Figure 3 It is a timing diagram of the BFBIC module control signal of the present invention.

[0090] Figure 4 It is the operating condition diagram of the BFBIC module of the present invention.

[0091] Figure 5 It is a fitting diagram of the bridge arm IGBT characteristic curve of the present invention.

[0092] Figure 6It is a fitting diagram of the bridge arm FWD characteristic curve of the present invention.

[0093] Figure 7 It is a fitting diagram of the clamped IGBT characteristic curve of the present invention.

[0094] Figure 8 It is a fitting diagram of the clamped FWD characteristic curve of the present invention.

[0095] Fig. 9 It is a characteristic curve fitting diagram of the secondary side FWD module of the present invention.

[0096] Fig.10 It is a layered structure diagram of the IGBT module of the present invention.

[0097] Fig.11 It is a layered structure diagram of the FWD module of the present invention.

[0098] Fig.12 It is a logical connection relationship diagram of the Boost full-bridge boost isolation converter combined DC / DC converter of the present invention.

[0099] Fig.13 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0100] The present invention will be described in detail below based on the accompanying drawings and preferred embodiments, and the purpose and effects of the present invention will become more clear. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0101] Example 1, please refer to Fig.13 The present invention provides a DC / DC converter reliability assessment method, comprising:

[0102] Construct an electro-thermal coupling model of the power switch module of the Boost full-bridge boost isolation converter BFBIC combined DC / DC converter topology to obtain the power loss and junction temperature changes;

[0103] Build a life prediction model based on junction temperature changes, and calculate the failure rate using a fatigue damage accumulation model;

[0104] A calculation model for the shutdown probability of series / parallel modules is established based on the failure rate, and the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter is evaluated using the improved reliability block diagram method.

[0105] Embodiment 2, the present invention provides a DC / DC converter reliability assessment method, specifically comprising:

[0106] Based on the analysis of the topological structure and operating conditions of the Boost full-bridge boost isolation converter combined DC / DC converter, an electrothermal coupling model of its power switch module is constructed to analyze its power loss and junction temperature changes.

[0107] Combine the life prediction model and fatigue damage accumulation model of key modules to calculate their failure rate;

[0108] The reliability of the Boost full-bridge boost isolation converter combined DC / DC converter is evaluated using the improved reliability block diagram method.

[0109] Furthermore, based on the analysis of the Boost full-bridge boost isolation converter combined DC / DC converter topology and operating conditions, an electrothermal coupling model of its power switch module is constructed to analyze its power loss and junction temperature change. The steps are:

[0110] Furthermore, based on the analysis of the Boost full-bridge boost isolation converter combined DC / DC converter topology and operating conditions, an electrothermal coupling model of its power switch module is constructed to analyze its power loss and junction temperature change. The steps are:

[0111] Step 1: Analyze the topology and operating conditions of the BFBIC combined DC / DC converter.

[0112] For the DC collection system of wind farms, high efficiency, high reliability topology, voltage stability control and modular balancing control are the basic technical requirements of DC / DC converters. To this end, this paper adopts a DC / DC converter topology based on Boost full-bridge boost isolation converter. The BFBIC module topology is as follows Figure 1 As shown. In order to realize high-power application of DC / DC converter, hybrid two-stage modular integration technology of input parallel and output series (IPOS) and input parallel and output parallel (IPOP) is used to improve the transmission power to meet the requirements of DC voltage level and DC / DC converter capacity. The topology of BFBIC combined DC / DC converter is shown as follows: Figure 2 shown.

[0113] When the DC / DC converter is operating normally, the trigger signals of S1 and S4 in the IGBT are the same, the trigger signals of S2 and S3 are the same, the trigger signals of S1 and S4 are half a cycle ahead of the trigger signals of S2 and S3, and the trigger signal of Sc is obtained by performing AND-NOT operations on the trigger signals of S1 and S4 and the trigger signals of S2 and S3. It can be clearly seen that the conduction time of the Sc trigger signal is shorter than that of the trigger signals of S1 and S4 (S2 and S3), in order to avoid transient overvoltage and thus make the inductor L boost Release energy. Based on the above, the six operating conditions of the BFBIC module are analyzed, and it is assumed that the boost inductor Lboost is large enough, its current remains unchanged, the clamping branch capacitor Cc is large enough to keep the bridge arm voltage constant, and all switching elements are ideal elements. The operating conditions of the BFBIC module are as follows: Figure 3 , Figure 4 shown.

[0114] Step 2: Establish the power loss model of the IGBT module and the FWD module. When calculating the power loss of the IGBT module, only the on-state loss and switching loss of the IGBT chip, as well as the on-state loss and turn-off loss of the FWD need to be considered. The power loss model of the FWD module is the same as the power loss of the FWD in the IGBT module power loss model.

[0115] (1) IGBT conduction loss

[0116] P CL,I =V ce ·i c,I ·D

[0117] V ce (i c ,T I )=V ce0 (T I )+r ce (T I )i c

[0118] V ce0 (T I )=V ce，25℃ +TC V (T I -25)

[0119] r ce (T I )=r ce，25℃ +TC r (T I -25)

[0120]

[0121] Where Vce is the collector-emitter saturation voltage drop, ic, I is the collector current, and D is the duty cycle; Where: T I is the junction temperature; V ce0 is the initial saturation pressure drop; r ce is the on-resistance; V ce,25℃ is the saturation voltage drop of IGBT at 25°C; r ce,25℃ is the on-resistance of the IGBT at 25°C; TC V and TC r Respectively represent V ce and r ce The temperature coefficient of; D(t) is the duty cycle function (time domain); k pi The value is 0.965; k di The value is 0.00065; k pv The value is 0.003; T i The value is 0.0045; △U is the difference between the input DC voltage and the reference voltage; δ(t) is the impulse function; 1(t) is the unit step function.

[0122] (2) IGBT switching losses

[0123]

[0124] P sw,I =P on,I +P off,I

[0125] In the formula, f sw is the switching frequency, E on,I 、E off,I are the turn-on and turn-off loss energies of the IGBT, U dc 、i c,I is the operating voltage and current of IGBT, U N 、i N is the rated voltage and current, K on,I , K off,I K is the influence coefficient of IGBT gate resistance on turn-on and turn-off losses; T,I is the temperature correction coefficient of switching energy loss.

[0126] (3) IGBT total power loss P I for

[0127] P I =P CL,I +P sw,I

[0128] (4) FWD conduction loss

[0129] P CL,F =V F·i c,F ·(1-D)=f(i c,F ,T F )·i c,F (1-D)

[0130] Where: T F is the FWD junction temperature.

[0131] (5) FWD turn-off loss

[0132]

[0133] Where: E off,F is the energy loss of FWD reverse recovery; K off,F K is the influence coefficient of FWD forward resistance on turn-off loss; T,F is the temperature coefficient of the turn-off energy loss.

[0134] (6) Total FWD loss P F for

[0135] P F =P CL,F +P sw,F

[0136] Based on the above steps, the output characteristic curves of the IGBT and FWD at different temperatures in the primary bridge arm IGBT module and the clamped IGBT manual in the DC / DC converter are fitted in three dimensions. The fitting results are shown in the figure. Figures 5 to 8 As shown, the analytical expression is:

[0137] V ceQB =(0.4808·(i ceQB )^(1 / 10))+3.203×10 -6 ·i ceQB ·T ceQB -0.0007892 T ceQB +0.0003977·i ceQB +0.1257

[0140] V FQB =(0.09699·(i FQB )^(1 / 3))+1.149×10 -7 ·i FQB ·T FQB -0.0007892 T FQB +0.0003977·i FQB +0.1257

[0143] V ceQW =(0.2856·(i ceQW )^(1 / 5))+3.776×10 -6 ·i ceQW ·T ceQW -0.0006428·T ceQW +0.0003313·i ceQW +0.1184

[0146] V FQW =(0.03134·(i FQW )^(1 / 2))+1.047×10 -6 ·i FQW ·T FQW -0.001728·T FQW +7.459×10 -5 ·i FQW +0.5685

[0149] Where V ceQB is the collector-emitter voltage of the primary-side bridge arm IGBT module; i ceQB is the collector current of the primary-side bridge arm IGBT module; T ceQB is the junction temperature of the primary-side bridge arm IGBT module; V FQB is the forward voltage of the primary bridge arm FWD module; i FQB is the forward current of the primary bridge arm FWD module; T FQB is the junction temperature of the primary bridge arm FWD module; V ceQW is the collector-emitter voltage of the primary-side clamped IGBT module; i ceQW is the collector current of the primary side clamped IGBT module; T ceQW is the junction temperature of the primary-side clamped IGBT module; V FQW is the forward voltage of the primary side clamped FWD module; i FQW is the forward current of the primary-side clamped FWD module; T FQW is the junction temperature of the primary-side clamped FWD module.

[0150] Based on this, the power loss (average value) of the primary-side bridge arm IGBT module and the primary-side clamp IGBT module can be calculated according to the IGBT module loss model, as shown in Table 1.

[0151] Table 1 Primary side IGBT module power loss

[0152]

[0153]

[0154] The output characteristic curve of the secondary side FWD module in the DC / DC converter at different temperatures is fitted in three dimensions. The fitting results are shown in Fig. 9 As shown, the analytical expression is:

[0155] V FDY =(0.1628·(i FDY )^(1 / 2))+2.908×10 -6

[0156] ·i FDY ·T FDY +0.6571

[0157] Based on the above formula, the power loss (average value) of the FWD module can be calculated according to the FWD module loss model, as shown in Table 2.

[0158] Table 2 Power loss of FWD module

[0159]

[0160] Step 3: Based on the losses of the IGBT module and the FWD module, the junction temperature evaluation model of the IGBT module and the FWD module is constructed using the thermoelectric analogy theory.

[0161] (1) The Foster thermal network model is used to evaluate the junction temperature of the IGBT module and the FWD module. First, the thermal parameters are converted into electrical parameters using the thermoelectric analogy theory, and then the problems in the thermal network are solved using the electrical network theory. The thermal-electric parameter conversion relationship is shown in Table 3. The layered structure of the IGBT module and the FWD module is shown in Fig.10 , Fig.11 shown.

[0162] Table 3 Thermal-electrical parameter conversion relationship

[0163]

[0164] (2) In the Foster thermal network, the chip-to-shell R thjc It is equivalent to a fourth-order RC electrical network, the shell-heat sink R thch and radiator-ambient R thha A first-order RC electrical network is used.

[0165]

[0166] τ i =R i ·C i

[0167] T I =P I ·(Z thjc_T +Z thch_T )+(P I +P F )·Z thha +T a

[0168] T F =P F ·(Z thjc_D +Z thch_D )+(P I +P F )·Z thha +T a

[0169] T D,F =P F ·(Z 0jc_D +Z 0cs_D )+P F ·Z 0sa +T a

[0170] Where: Z is thermal impedance; n is the order of Foster equivalent thermal network model; τ i is the time constant of the i-th order Foster equivalent thermal network model; R i , C i are the equivalent thermal resistance and thermal capacitance of chip-to-shell respectively; Z thjc_T is the thermal impedance of the IGBT chip-to-case in the IGBT module; Z thch_T is the thermal impedance of the IGBT case-heat sink in the IGBT module; Z thjc_D is the thermal impedance of the FWD chip-to-shell in the IGBT module; Z thch_D is the thermal impedance of the FWD tube case-heat sink in the IGBT module; Z thta is the IGBT module heat sink-environment thermal impedance; Z 0jc_D is the FWD module chip-to-case thermal impedance; Z 0cs_D is the thermal impedance of the FWD module shell and heat sink; Z 0sa is the FWD module heat sink-environment thermal impedance; T a is the ambient temperature.

[0171] Based on the above steps and the calculated power loss results of each module of the DC / DC converter, the junction temperature value of each module can be obtained, as shown in Table 4.

[0172] Table 4 Junction temperature values ​​of each module of DC / DC converter

[0173]

[0174] Furthermore, the calculation steps of the failure rate of the key module by combining the life prediction model and fatigue damage accumulation model are as follows:

[0175] Step 1: Use the rain flow algorithm to accurately count the number of module fluctuations at different junction temperature means and fluctuation amplitudes within a certain period of time, then calculate the damage degree to complete the life assessment.

[0176] Step 2: Use the Coffin-Manson-Arrheniu analytical model, which has high reliability assessment accuracy and easy model parameter acquisition, to predict the life of the IGBT module and FWD module.

[0177]

[0178] Where: ΔT j Indicates the junction temperature difference, T m Represents the average junction temperature, N f Indicates the working condition ΔT j and T m The failure cycles under the condition are as follows. α and β are module parameters, and their values ​​are 3.025×10 5 , -0.5039, E a is the activation energy, and its value is 9.89×10 -20 J, K B is the Boltzmann constant, which is 1.382×10 -23 J / K.

[0179] Step 3: Use the linear fatigue damage accumulation model to calculate the failure rate of the IGBT module and FWD module. The results are shown in Table 5. The calculation formula is:

[0180]

[0181] Where: N i is the number of cycles under working condition i. X To evaluate the failure rate of type X modules.

[0182] Table 5 Lifespan and failure rate of each module

[0183]

[0184] Furthermore, the calculation steps for evaluating the reliability of the DC / DC converter using the improved reliability block diagram method are as follows:

[0185] Step 1: Establish a general calculation model for the outage probability of series / parallel modules;

[0186] (1) Series modules

[0187] In a series module, if any series submodule in the system fails, the entire system will be shut down. Only when all series submodules in the system are operating normally can the system work normally. The general calculation model for the shutdown probability of a series module with N components is:

[0188]

[0189] Where: series is the failure rate of the modules in series in non-redundancy mode; μ series is the repair rate of the series connected modules in the non-redundant mode; i is the failure rate of the ith series submodule; μ i is the repair rate of the ith series submodule; T MTTR,i is the repair time of the i-th series submodule.

[0190] (2) Parallel modules

[0191] In a parallel module, only when all parallel submodules fail will the entire system shut down. The general calculation model for the shutdown probability of a parallel module with N components is:

[0192]

[0193] Where: parallel is the failure rate of parallel modules in non-redundant mode; μ parallel is the repair rate of parallel modules in non-redundant mode; T MTTR,i is the repair time of the ith parallel submodule; μ i is the repair rate of the i-th parallel submodule.

[0194] Step 2: Divide the Boost full-bridge boost isolation converter combined DC / DC converter into four hierarchical modules, and construct the outage probability model of the four hierarchical modules of the DC / DC converter. The logical connection relationship between the internal components of each hierarchical module is as follows: Fig.12 shown.

[0195] (1) In the four-level BFBIC module, all components are connected in series. If any component fails, the entire BFBIC module cannot operate normally. The outage probability model of the four-level BFBIC module is:

[0196]

[0197]

[0198] Where: BFBIC and μ BFBIC are the failure rate and repair rate of the four-level module BFBIC module respectively; IGBT, C , T , FWD , L They are the failure rates of IGBT module, capacitor, transformer T, FWD module, and inductor respectively; T C 、T IGBT 、T T 、T FWD 、T L They are the average repair time of capacitors, IGBT modules, transformer T, FWD modules, and inductors respectively; F is the number of capacitors; U is the number of IGBT modules; Q is the number of transformers; V is the number of FWD modules; and Z is the number of inductors.

[0199] (2) In the three-level IPOS module, multiple BFBIC modules are connected in parallel and in series. The failure of any BFBIC module will cause the failure of the entire IPOS module. The outage probability model of the IPOS module is:

[0200]

[0201] Where: IPOS and μ IPOS are the failure rate and repair rate of IPOS modules respectively, and θ is the number of BFBIC modules.

[0202] (3) In the secondary module IPOP module, each IPOS module is connected in parallel to realize the high-power application of DC / DC converter. Its outage probability model is:

[0203]

[0204] Where: IPOP and μ IPOP They are the failure rate and repair rate of IPOP module respectively; is the number of IPOS modules.

[0205] (4) In the first-level module Boost full-bridge boost isolation converter combined DC / DC converter, since the hardware main circuit system and the software control system are in a series logical relationship, if any system fails, the entire Boost full-bridge boost isolation converter combined DC / DC converter cannot operate normally. Since the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter mainly depends on the hardware main circuit and its connection method, and the reliability of its control system is difficult to quantify, this paper ignores the impact of the software control system on the reliability of the equipment when evaluating the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter, and only considers the impact of the hardware main circuit on the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter. Its outage probability model is:

[0206] λ DC / DC =λ IPOP

[0207] μ DC / DC =μ IPOP

[0208] Where: DC / DC and μ DC / DC They are the failure rate and repair rate of the first-level module Boost full-bridge boost isolation converter combined DC / DC converter.

[0209] (5) Assuming that the BFBIC module topology remains unchanged, the calculation formula for the Boost full-bridge boost isolation converter combined DC / DC converter topology at different voltage levels is:

[0210]

[0211] Where: θ k The number of IPOS modules in the Boost full-bridge boost isolation converter combined DC / DC converter; is the number of IPOP modules in the Boost full-bridge boost isolation converter combined DC / DC converter; U DC / DC P is the output voltage of the Boost full-bridge boost isolation converter combined DC / DC converter; DC / DC is the output power of the Boost full-bridge boost isolation converter combined DC / DC converter; U BFBIC is the output voltage of the BFBIC module; P BFBIC is the output power of the BFBIC module.

[0212] This section uses the aforementioned Boost full-bridge boost isolation converter combined DC / DC converter based on improved RBD to calculate the failure rate and repair rate of each module component.

[0213] (1) The failure rate and repair rate of each component of the four-level module BFBIC module are shown in Table 6.

[0214] Table 6 Failure rate and repair rate of each component of the four-level module BFBIC module

[0215]

[0216] (2) The failure rate and repair rate of each component of the three-level module IPOS module are shown in Table 7.

[0217] Table 7 Failure rate and repair rate of each component of the three-level module IPOS module

[0218]

[0219] (3) The failure rate and repair rate of each component of the secondary module IPOP module are shown in Table 8.

[0220] Table 8 Failure rate and repair rate of each component of the secondary module IPOP module

[0221]

[0222] (4) The failure rate and repair rate of each component of the first-stage module Boost full-bridge boost isolation converter combined DC / DC converter are shown in Table 9.

[0223] Table 9 Failure rate and repair rate of each component of the first-level module Boost full-bridge boost isolation converter combined DC / DC converter

[0224]

[0225] In yet another embodiment of the present invention, a DC / DC converter reliability assessment system is provided, which can be used to implement the above-mentioned DC / DC converter reliability assessment method. Specifically, the system includes:

[0226] The junction temperature change output module is used to construct the electrothermal coupling model of the power switch module of the Boost full-bridge boost isolation converter BFBIC combined DC / DC converter topology structure to obtain the power loss and junction temperature change;

[0227] Failure rate calculation module, used to build a life prediction model based on junction temperature changes and calculate the failure rate in combination with the fatigue damage accumulation model;

[0228] The evaluation output module is used to establish a calculation model for the shutdown probability of series / parallel modules based on the failure rate, and to evaluate the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter using the improved reliability block diagram method.

[0229] The division of modules in the embodiments of the present invention is schematic and is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present invention may be integrated into one processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules may be implemented in the form of hardware or in the form of software functional modules.

[0230] In another embodiment of the present invention, a computer device is provided, the computer device comprising a processor and a memory, the memory being used to store a computer program, the computer program comprising program instructions, and the processor being used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, which are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions in a computer storage medium to implement a corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a DC / DC converter reliability assessment method.

[0231] In another embodiment of the present invention, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both the built-in storage medium in the computer device and the extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the reliability evaluation method of a DC / DC converter in the above embodiment.

[0232] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0233] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0234] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0235] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0236] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A DC / DC converter reliability assessment method, characterized in that: include: Construct an electro-thermal coupling model of the power switch module of the Boost full-bridge boost isolation converter BFBIC combined DC / DC converter topology to obtain the power loss and junction temperature changes; Build a life prediction model based on junction temperature changes, and calculate the failure rate using a fatigue damage accumulation model; A calculation model for the shutdown probability of series / parallel modules is established based on the failure rate, and the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter is evaluated using the improved reliability block diagram method.

2. A DC / DC converter reliability assessment method according to claim 1, characterized in that: Construct an electrothermal coupling model of the power switch module of the Boost full-bridge boost isolation converter BFBIC combined DC / DC converter topology, including: For the Boost full-bridge step-up isolation converter combined DC / DC converter, a hybrid two-stage modular integration of input parallel connection, output series connection and input parallel connection, output parallel connection is adopted.

3. A DC / DC converter reliability assessment method according to claim 1, characterized in that: Get power loss and junction temperature changes, including: Establish power loss models of insulated gate bipolar transistor IGBT module and forward blocking diode FWD module. The power loss model of FWD module is the same as the power loss of FWD in the power loss model of IGBT module. (1) IGBT conduction loss P CL,I =V ce ·i c,I ·D V ce (i c ,T I )=V ce0 (T I )+r ce (T I )i c V ce0 (T I )=V ce，25℃ +TC V (T I -25) r ce (T I )=r ce，25℃ +TC r (T I -25) Where Vce is the collector-emitter saturation voltage drop, i c,I is the collector current, D is the duty cycle; where: T I is the junction temperature; V ce0 is the initial saturation pressure drop; r ce is the on-resistance; V ce,25℃ is the saturation voltage drop of IGBT at 25°C; r ce,25℃ is the on-resistance of the IGBT at 25°C; TC V and TC r Respectively represent V ce and r ce The temperature coefficient of; D(t) is the duty cycle function (time domain); k pi The value is 0.965; k di The value is 0.00065; k pv The value is 0.003; T i The value is 0.0045; △U is the difference between the input DC voltage and the reference voltage; δ(t) is the impulse function; 1(t) is the unit step function; (2) IGBT switching losses P sw,I =P on,I +P off,I In the formula, f sw is the switching frequency, E on,I 、E off,I are the turn-on and turn-off loss energies of the IGBT, U dc 、i c,I is the operating voltage and current of IGBT, U N 、i N is the rated voltage and current, K on,I , K off,I K is the influence coefficient of IGBT gate resistance on turn-on and turn-off losses; T,I is the temperature correction coefficient of switching energy loss; (3) IGBT total power loss P I P I =P CL,I +P sw,I (4) FWD conduction loss P CL,F =V F ·i c,F ·(1-D)=f(i c,F ,T F )·i c,F ·(1-D) Where: T F is the FWD junction temperature; (5) FWD turn-off loss Where: E off,F is the energy loss of FWD reverse recovery; K off,F K is the influence coefficient of FWD forward resistance on turn-off loss; T,F is the temperature coefficient of the turn-off energy loss; (6) Total FWD loss P F for P F =P CL,F +P sw,F Based on the losses of IGBT modules and FWD modules, the junction temperature evaluation model of IGBT modules and FWD modules is constructed using thermoelectric analogy theory; The Foster thermal network model is used to evaluate the junction temperature of the IGBT module and the FWD module. First, the thermal parameters are converted into electrical parameters using the thermoelectric analogy theory. The chip-to-case R in the IGBT module is connected in the Foster thermal network. thjc It is equivalent to a fourth-order RC electrical network, the shell-heat sink R thch and radiator-ambient R thha A first-order RC electrical network is used; t i =R i ·C i T I =P I ·(Z thjc_T +Z thch_T )+(P I +P F )·Z thha +T a T F =P F ·(Z thjc_D +Z thch_D )+(P I +P F )·Z thha +T a T D,F =P F ·(Z 0jc_D +Z 0cs_D )+P F ·Z 0sa +T a Where: Z is thermal impedance; n is the order of Foster equivalent thermal network model; τ i is the time constant of the i-th order Foster equivalent thermal network model; R i , C i are the equivalent thermal resistance and thermal capacitance of chip-to-shell respectively; Z thjc_T is the thermal impedance of the IGBT chip-to-case in the IGBT module; Z thch_T is the thermal impedance of the IGBT case-heat sink in the IGBT module; Z thjc_D is the thermal impedance of the FWD chip-to-shell in the IGBT module; Z thch_D is the thermal impedance of the FWD tube case-heat sink in the IGBT module; Z thta is the IGBT module heat sink-environment thermal impedance; Z 0jc_D is the FWD module chip-to-case thermal impedance; Z 0cs_D is the thermal impedance of the FWD module shell and heat sink; Z 0sa is the FWD module heat sink-environment thermal impedance; T a is the ambient temperature.

4. A DC / DC converter reliability assessment method according to claim 1, characterized in that: A life prediction model is built based on the change of junction temperature, including: The rain flow algorithm is used to accurately count the number of module fluctuations at different junction temperature averages and fluctuation amplitudes within a certain period of time, and then the damage degree is calculated to complete the life assessment. The Coffin-Manson-Arrheniu analytical model is used to predict the life of IGBT modules and FWD modules. Where: ΔT j Indicates the junction temperature difference, T m Represents the average junction temperature, N f Indicates the working condition ΔT j and T m The number of failure cycles under the condition of α and β are module parameters, and their values ​​are 3.025×105 and -0.5039 respectively. Ea ​​is the activation energy, and its value is 9.89×10-20J. KB is the Boltzmann constant, and its value is 1.382×10-23J / K.

5. A DC / DC converter reliability assessment method according to claim 4, characterized in that: Failure rate calculation combined with fatigue damage accumulation model, including: The linear fatigue damage accumulation model is used to calculate the failure rate of the IGBT module and FWD module. The calculation formula is: Where: N i is the number of cycles under working condition i; X To evaluate the failure rate of type X modules.

6. A DC / DC converter reliability assessment method according to claim 1, characterized in that: A calculation model for the probability of shutdown of series / parallel modules is established based on the failure rate, including: In the series module, the calculation model of the outage probability of the module composed of N components in series is: Where: λseries is the failure rate of the series modules in the non-redundant mode; μseries is the repair rate of the series modules in the non-redundant mode; λ i is the failure rate of the ith series submodule; μ i is the repair rate of the ith series submodule; TMTTR,i is the repair time of the ith series submodule; In the parallel module, the calculation model of the outage probability of the parallel module with N components is: Where: parallel is the failure rate of parallel modules in non-redundant mode; μ parallel is the repair rate of the parallel module in the non-redundant mode; TMTTR,i is the repair time of the i-th parallel submodule; μ i is the repair rate of the i-th parallel submodule.

7. A DC / DC converter reliability assessment method according to claim 6, characterized in that: The reliability of the boost full-bridge boost isolation converter combined DC / DC converter is evaluated using the improved reliability block diagram method, including: The Boost full-bridge boost isolation converter combined DC / DC converter is divided into four hierarchical modules, and the outage probability model of the four hierarchical modules of the DC / DC converter is constructed: In the four-level BFBIC module, all components are connected in series; the outage probability model of the four-level BFBIC module is: Where: BFBIC and μ BFBIC are the failure rate and repair rate of the four-level module BFBIC module respectively; IGBT , C , T , FWD , L They are the failure rates of IGBT module, capacitor, transformer T, FWD module, and inductor respectively; T C , T IGBT , T T , T FWD , T L They are the average repair time of capacitors, IGBT modules, transformer T, FWD modules, and inductors respectively; F is the number of capacitors; U is the number of IGBT modules; Q is the number of transformers; V is the number of FWD modules; and Z is the number of inductors; In the three-level IPOS module, multiple BFBIC modules are connected in parallel and then in series. The outage probability model of the IPOS module is: Where: IPOS and μ IPOS are the failure rate and repair rate of IPOS modules, respectively; θ is the number of BFBIC modules; In the secondary module IPOP module, each IPOS module is connected in parallel to realize the high-power application of the DC / DC converter. Its outage probability model is: Where: IPOP and μ IPOP They are the failure rate and repair rate of IPOP module respectively; is the number of IPOS modules; In the primary module Boost full-bridge boost isolation converter combined DC / DC converter, when evaluating the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter, the influence of the hardware main circuit on the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter is considered; its outage probability model is: l DC / DC =λ IPOP m DC / DC =μ IPOP Where: DC / DC and μ DC / DC They are the failure rate and repair rate of the primary module DC / DC converter respectively; Assuming that the BFBIC module topology remains unchanged, the calculation formula for the Boost full-bridge boost isolation converter combined DC / DC converter topology at different voltage levels is: Where: θ k is the number of IPOS modules in the DC / DC converter; ω is the number of IPOP modules in the Boost full-bridge boost isolation converter combined DC / DC converter; U DC / DC P is the output voltage of the Boost full-bridge boost isolation converter combined DC / DC converter; DC / DC is the output power of the Boost full-bridge boost isolation converter combined DC / DC converter; U BFBIC is the output voltage of the BFBIC module; P BFBIC is the output power of the BFBIC module.

8. A DC / DC converter reliability assessment system, characterized in that: include: The junction temperature change output module is used to construct the electrothermal coupling model of the power switch module of the Boost full-bridge boost isolation converter BFBIC combined DC / DC converter topology structure to obtain the power loss and junction temperature change; Failure rate calculation module, used to build a life prediction model based on junction temperature changes and calculate the failure rate in combination with the fatigue damage accumulation model; The evaluation output module is used to establish a calculation model for the shutdown probability of series / parallel modules based on the failure rate, and to evaluate the reliability of the Boost full-bridge boost isolation converter combined DC / DC converter using the improved reliability block diagram method.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the DC / DC converter reliability evaluation method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of a DC / DC converter reliability evaluation method as claimed in any one of claims 1 to 7 are implemented.

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