A method for drawing safe operating area for high-voltage and high-power thyristor applications

Abstract

The present invention discloses a method for drawing a safe operating area for high-voltage and high-power thyristor applications, which is performed in the following steps: Step S1: establishing a power loss model of the thyristor under different load currents, gate trigger conditions, and different operating frequencies, and obtaining a thyristor power loss curve through electric and thermal co-simulation; Step S2: establishing a pressure F at both ends of the thyristor under a certain initial installation pressure based on the thermal expansion theory; N and the radiator temperature T h The functional relationship F N (T h ); The present invention is used to determine the application safe operating area of ​​high-voltage and high-power thyristors, thereby helping to reduce system operating costs and achieve full and reasonable utilization of large-capacity thyristors, and has good practicality.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a method for drawing a safe operating area for high-voltage and high-power thyristor applications. Background Art

[0002] High voltage direct current (HVDC) technology not only offers the advantages of low losses and a small footprint, but also possesses significant technical and economic advantages in long-distance, high-capacity power transmission applications, playing a vital role in my country's smart grid development. Converter valves are core equipment in HVDC projects. Thyristors, currently one of the power electronic devices with the highest withstand voltage and largest output capacity, are still the dominant HVDC converter valves. As the core component of converter valves, the stability of their electrical characteristics is crucial for the reliable operation of the entire converter valve system and, ultimately, the entire power system.

[0003] As voltage levels and transmission capacities of flexible direct current (HVDC) transmission systems continue to increase, performance requirements for large-capacity thyristor (SCR) power devices in converter valves are also increasing. The selection of large-capacity thyristors has become a significant factor affecting the reliability and cost of the entire HVDC transmission project. Currently, to ensure the safe and reliable operation of power devices and systems, extensive, high-margin, and multi-redundant design approaches are often adopted, sacrificing cost to ensure reliable operation of converter valve systems. Due to the press-fit packaging structure of large-capacity thyristors, water-cooled heat sinks are often used to effectively dissipate heat. This high-margin, multi-redundant design approach significantly increases the cost, size, and weight of the converter system. Therefore, determining the safe operating area (SAA) for high-voltage, high-power thyristor applications is crucial for significantly reducing system costs and ensuring the full and rational utilization of large-capacity thyristors while ensuring the safe and reliable operation of the HVDC transmission system. Summary of the Invention

[0004] The present invention aims to provide a method for mapping the safe operating area (SAA) for high-voltage, high-power thyristor applications. This method is used to determine the SAA for high-voltage, high-power thyristor applications, thereby helping to reduce system operating costs and achieve full and reasonable utilization of large-capacity thyristors, with excellent practicality.

[0005] The technical solution of the present invention is a method for drawing a safe operating area for high-voltage and high-power thyristor applications, which is performed according to the following steps:

[0006] Step S1: establishing a power loss model for the thyristor under different load currents, gate trigger conditions, and operating frequencies, and obtaining a thyristor power loss curve through electrothermal co-simulation;

[0007] Step S2: Based on the thermal expansion theory, establish the pressure F at both ends of the high-voltage and high-power thyristor under a certain initial installation pressure. N and the radiator temperature T h The functional relationship F N (T h );

[0008] Step S3: In the thyristor's allowable installation pressure range F N,min <F N <F N,max The thermal resistance Z between the junction and the heat sink of the thyristor is measured at different pressures. th_jh According to the pressure at both ends of the thyristor and the measured junction-to-heat sink thermal resistance under the corresponding conditions, the junction-to-heat sink thermal resistance Z is obtained by data fitting. th_jh With pressure F N The relationship curve of the junction to heat sink thermal resistance and pressure is further obtained as a function of Z th_jh (F N ), according to the pressure F in step S2 N and the radiator temperature T h The functional relationship F N (T h ), and finally get the thermal resistance from junction to heat sink Z th_jh With pressure F N And the radiator temperature T h Function expression Z th_jh (T h ,F N )

[0009] Step S4: According to the functional relationship F in step S2 N (T h ), obtain the initial installation pressure F N_0 The allowable range of the radiator temperature T corresponding to the allowable installation pressure range of the thyristor is h_min <T h <T h_max ;

[0010] Step S5: Calculating a cooling power curve of the radiator of the high-voltage and high-power thyristor at the corresponding radiator temperature according to the allowable range of the radiator temperature obtained in step S4;

[0011] Step S6: Obtaining the thyristor limit power loss curve corresponding to the cooling power curve at a certain radiator temperature in step S5 according to the limit thermal balance theory, determining whether there is a tangent point between the thyristor power loss curve and the cooling power curve of the radiator; if not, searching for a power loss curve tangent to the cooling power curve; if so, proceeding to the next step;

[0012] Step S7: Obtain the radiator temperature T according to the intersection point of the limit power loss curve and the radiator cooling power curve in step S6 h And the corresponding operating current I of the thyristor AK , and draw the thyristor's application safe operating area T h -I AK .

[0013] In the above-mentioned method for drawing the safe operating area for high-voltage and high-power thyristor applications, the power loss model and power loss curve in step S1 are obtained through an electrothermal joint simulation model.

[0014] In the above method for drawing the safe operating area of ​​high-voltage and high-power thyristor applications, the pressure F at both ends of the thyristor in step S2 is N and the radiator temperature T h The functional relationship F N (T h ) is: F N =k×(T h -T h,min0 )+F0, where k is the coefficient of pressure and radiator temperature, T h is the temperature of the radiator, F0 is the initial stress of the thyristor of the converter valve when it is installed, T h,min0 It is the radiator temperature corresponding to the initial installation pressure F0.

[0015] In the aforementioned method for drawing the safe operating area for high-voltage and high-power thyristor applications, the gate trigger conditions in step S1 include trigger current, trigger time, and trigger angle.

[0016] Compared with the existing technology, the present invention can obtain the application safe operating area of ​​high-voltage and high-power thyristors, thereby helping to reduce system operating costs and achieve full and reasonable utilization of large-capacity thyristors. It has good practicality, and the acquisition process uses power loss, pressure at both ends of the thyristor, radiator temperature and radiator thermal resistance as the calculation basis, fully considering various parameters in the operation of the thyristor, so that the results of the application safe operating area have sufficient reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the steps of the present invention;

[0018] Figure 2 This is a schematic diagram of the ultimate thermal balance analysis of the thyristor of the present invention;

[0019] Figure 3 Schematic diagram of the relationship between the pressure at both ends of the press-fit thyristor and the temperature of the heat sink of the present invention;

[0020] Figure 4 This is a schematic diagram showing how the pressure at both ends of the thyristor changes with the temperature of the radiator;

[0021] Figure 5 Schematic diagram of the internal packaging structure and thermal resistance network of the press-fit thyristor of the present invention;

[0022] Figure 6 Schematic diagram showing the change of the thermal resistance of the thyristor junction-heat sink with the change of the pressure at both ends of the thyristor junction;

[0023] Figure 7 Schematic diagram of the internal feedback mechanism when the power loss of the press-fit thyristor increases according to the present invention;

[0024] Figure 8 Schematic diagram of the ultimate heat balance analysis under load conditions of the present invention;

[0025] Figure 9 It is a schematic diagram of the safe working area of ​​the thyristor application of the converter valve of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and examples, but they are not intended to limit the present invention.

[0027] Embodiment: A method for drawing a safe operating area for high-voltage and high-power thyristor applications, as shown in the attached Figure 1 As shown, follow the steps below:

[0028] Step S1: establishing a power loss model for the thyristor under different load currents, gate trigger conditions, and operating frequencies, and obtaining a thyristor power loss curve through electrothermal co-simulation;

[0029] The operating frequency of thyristors is relatively low. When calculating their power loss, only the conduction loss is often considered, and the switching loss of the thyristors is ignored. Since the thyristors in the HVDC transmission converter valves are subjected to high voltage (several kV) in the off state, the on-state voltage when conducting is only a few volts, and the on-state current is as high as several thousand amperes, the electrothermal simulation model is used to obtain the power loss of the thyristors and the power loss temperature curve of the thyristors. The method based on the electrothermal simulation model can obtain the loss of the thyristors under any working conditions, so as to analyze the limit thermal balance. According to the thermal balance theory, when the power loss P of the thyristor is heat Greater than the heat dissipation power P of the radiator sink When the thyristor is in thermal runaway state, it will eventually cause irreversible damage to the thyristor and then fail. Figure 2 As shown, when the heat dissipation power P sink2 The power loss of the thyristor P heat When they intersect at points A and B, below the first intersection point A, due to P heat >P sink2, so the working junction temperature of the thyristor continues to rise until the junction temperature reaches T1; between the first intersection A and the second intersection B, due to P heat <P sink2 , so the junction temperature of the thyristor will drop to T1 and reach a stable state; and above the second intersection B, due to P heat >P sink2 , and there is no third intersection point such that P heat =P sink2 , so the working junction temperature of the thyristor will continue to rise until thermal runaway failure occurs; when the thyristor power consumption curve is tangent to the heat dissipation power curve, that is, P heat With P sink1 Tangent point C means that points A and B coincide at point C. At this point, the situation corresponding to this point represents the worst heat dissipation condition. Therefore, when the power loss generated on the thyristor chip and the heat dissipation power between the heat sink cannot reach a thermal equilibrium state, the heat generated by the device cannot be completely dissipated, which will eventually lead to thermal runaway of the thyristor.

[0030] Step S2: Based on the thermal expansion theory, establish the pressure F at both ends of the high-voltage and high-power thyristor under a certain initial installation pressure. N and the radiator temperature T h The functional relationship F N (T h ); High-voltage and large-capacity thyristors use a press-fit packaging structure. According to the data sheet of the selected thyristor, find its minimum installation pressure F N,min and the maximum installation pressure F N,max ;

[0031] The heat dissipation of high-voltage and high-power thyristors is mainly achieved through water-cooled radiators. According to the theory of thermal expansion, under normal working conditions, the water temperature of the water-cooled radiator will increase due to the heat emitted by the thyristor, so the water-cooled heat sink will expand due to the increase in water temperature. Thermal expansion causes dimensional changes.

[0032] = δ = α × L × ΔT (1)

[0033] Where α is the thermal expansion coefficient of the water-cooled heat sink material, L is the initial length of the heat sink, and ΔT is the temperature change of the heat sink;

[0034] The volume change of the heat sink due to thermal expansion is: ΔV=βV0ΔT (2)

[0035] Where β is the volume expansion coefficient of the heat sink, and V0 is the initial volume of the heat sink. According to Hooke's law, within the range of elastic deformation of the material, the stress and strain in the solid material are in a linear relationship. Therefore, under the initial installation stress of the thyristor, the pressure at both ends of the thyristor will change with the temperature of the water-cooled radiator, as shown in the following figure. Figure 3As shown, when the thyristor is installed, the temperature of the water cooling radiator is at the minimum value T h,min , take the initial installation stress as the minimum installation stress F allowed in the thyristor data sheet N,min , as the heat sink temperature increases, the pressure at both ends of the thyristor gradually increases to the maximum installation stress F allowed by the thyristor. N,max When the water cooling radiator temperature is the maximum value of the radiator temperature T h,max ;

[0036] From the above, we can see that the maximum allowable temperature of the radiator depends on the initial installation pressure of the thyristor and the material of the radiator. When the initial installation stress is F N0 When the pressure at both ends of the thyristor reaches the maximum value, the corresponding radiator temperature is T h,max0 , so the relationship between the pressure at both ends of the converter valve thyristor and the radiator temperature can be expressed as:

[0037] F N =k×(T h -T h,min0 )+F0 (3)

[0038] Where k is the coefficient of pressure and radiator temperature, which depends on the material of the water-cooled radiator, T h is the temperature of the radiator, F0 is the initial stress of the thyristor of the converter valve when it is installed, T h,min0 The radiator temperature corresponding to the initial installation pressure F0 is measured. The pressure at both ends of the thyristor changes with the radiator temperature under different initial installation pressures, as shown in the attached figure. Figure 4 shown.

[0039] Step S3: In the thyristor's allowable installation pressure range F N,min <F N <F N,max The thermal resistance Z between the junction and the heat sink of the thyristor is measured at different pressures. th_jh According to the pressure at both ends of the thyristor and the measured junction-to-heat sink thermal resistance under the corresponding conditions, the junction-to-heat sink thermal resistance Z is obtained by data fitting. th_jh With pressure F N The relationship curve of the junction to heat sink thermal resistance and pressure is further obtained as a function of Z th_jh (F N ), according to the pressure F in step S2 N and the radiator temperature T h The functional relationship F N (T h ), and finally get the thermal resistance from junction to heat sink Z th_jh With pressure F N And the radiator temperature T h Function expression Zth_jh (T h ,F N );

[0040] High-voltage and large-capacity thyristors all use a press-fit packaging structure, which is essentially a stacked structure of multiple layers of different materials. Due to the non-ideal contact characteristics between different layers, the heat generated in the chip cannot be conducted smoothly between different layers, causing temperature differences between different contact layers. This effect can be represented by the concept of contact thermal resistance. The internal packaging structure of the press-fit thyristor and its thermal resistance network diagram are shown in the attached figure. Figure 5 As shown; the overall thermal resistance of different anode materials is Z th_bulk_A , the overall thermal resistance of different cathode materials is Z th_bulk_K , the overall contact thermal resistance of different layers of materials on the anode side is R th_cont_A , the overall contact thermal resistance of different layers of materials on the cathode side is R th_cont_K The contact thermal resistance between different materials is closely related to the microstructure of the interlayer contact surface. The contact surface realizes interlayer contact in the form of contact points. The thermal conductivity of the contact point is:

[0041]

[0042] Where k s is a constant, m and σ represent the equivalent surface slope and equivalent slope of the contact point respectively, p is the pressure at the contact point, H c is the hardness of the contact point;

[0043] From formula (4), we can see that when the pressure between the contact surfaces is greater, the thermal conductivity of the contact surface is greater, that is, the contact thermal resistance is smaller;

[0044] Thermal resistance Z from the thyristor junction to the heat sink th_jh and the pressure F across the thyristor N The relationship diagram is as shown in the attached Figure 6 As shown; In actual engineering applications, the thermal resistance Z from the thyristor junction to the heat sink is measured under different pressures. th_jh , according to the actual measurement results, similar Figure 6 The thermal resistance Z shown th_jh and the pressure F across the thyristor N The relationship curve and its function expression Z th_jh (F N );

[0045] During the actual operation of the thyristor, the thyristor chip generates heat due to power loss. heat When the chip working junction temperature T j Increase; According to the definition of thermal resistance, the temperature of the heat sink in steady state can be derived from the junction temperature of the thyristor as follows:

[0046] T h =T j -P heat ×Z th_jh (5)

[0047] Where T h is the radiator temperature;

[0048] Therefore, when the power loss P heat Increase the operating junction temperature T j When it increases, it will cause the radiator temperature T h From the above analysis, we can know that as the radiator temperature rises, the heat sink will expand due to heat, resulting in the pressure F at both ends of the thyristor N Increase, according to the Figure 6 It can be seen that the pressure F N The increase of the thermal resistance Z from the thyristor junction to the heat sink will th_jh Reduce, thereby suppressing the thyristor working junction temperature T j and the radiator temperature T h The rise of

[0049] The internal structure of the thyristor chip is PNPN, and the voltage of the ideal PN junction is U f and current I f The relationship can be expressed as:

[0050] Where k is the Boltzmann constant, q is the absolute value of the electron charge, E g is the semiconductor bandgap width, N C 、N V is the state density of the conduction band and valence band, N D is the doping concentration of the N region, D p is the diffusion coefficient of the P region, L p is the diffusion width, j is the current density;

[0051] From (6), we can see that the PN junction voltage U f It has a negative temperature coefficient relationship with temperature T, so when the working junction temperature T j When the voltage of the thyristor increases, the conduction voltage drop of the thyristor decreases, thereby suppressing its power loss P heat The increase in the thyristor load current causes the power loss P heat Increase, which in turn causes the operating junction temperature T j Increase, eventually leading to the pressure F at both ends of the thyristor N Increase, the increase of the pressure at both ends reduces the thermal resistance Z from the thyristor junction to the heat sink th_jh To suppress power loss P heat Increase and junction temperature T j The increase in Figure 7 As shown;

[0052] According to the attached Figure 3 and attached Figure 6 As shown, the thermal resistance Z from the thyristor junction to the heat sink th_jh is the radiator temperature T h and installation pressure F N The functional relationship of Z th_jh (T h ,F N ); If the above feedback mechanism is not considered, the safe operating area of ​​the thyristor application will be greatly reduced. When the power loss P is considered heat Increase the operating junction temperature T j Increased junction-to-heatsink thermal resistance Z th_jh When the feedback mechanism is reduced, even if the thyristor workload increases, the entire system can still be guaranteed to work safely as long as it does not exceed a certain range.

[0053] Step S4: According to the functional relationship F in step S2 N (T h ), obtain the initial installation pressure F N_0 The allowable range of the radiator temperature T corresponding to the allowable installation pressure range of the thyristor is h_min <T h <T h_max .

[0054] Step S5: Calculating a cooling power curve of the radiator of the high-voltage and high-power thyristor at the corresponding radiator temperature according to the allowable range of the radiator temperature obtained in step S4;

[0055] Step S6: According to the ultimate thermal balance theory, the ultimate power loss curve of the thyristor corresponding to the cooling power curve at a certain radiator temperature in step S5 is obtained, and it is determined whether there is a tangent point between the thyristor power loss curve and the cooling power curve of the radiator. If not, a power loss curve tangent to the cooling power curve is searched again. If so, the next step is performed.

[0056] During the actual installation of the thyristor, its initial installation pressure is F N_0 , according to formula (3), find the maximum allowable temperature T of the radiator under its initial installation conditions h_max and minimum installation temperature T h_min , within the allowable range of radiator temperature T h_min <T h <T h_max According to the attached Figure 2 The ultimate thermal balance theory shown in the figure is used to find the ultimate thermal balance conditions of the thyristor corresponding to different radiator temperatures, as shown in the attached figure. Figure 8As shown, only three radiator temperatures T are given h1 、T h2 、T h3 Under the thermal equilibrium situation, the traversal method can be used to find the heat sink temperature range T h_min <T h <T h_max All extreme thermal equilibrium operating points within.

[0057] Step S7: Obtain the radiator temperature T according to the intersection point of the limit power loss curve and the radiator cooling power curve in step S6 h And the corresponding operating current I of the thyristor AK , and draw the thyristor's application safe operating area T h -I AK .

[0058] As attached Figure 9 As shown, when the thyristor is in normal working state, the working current is I AK1 When the thyristor is in overload or short-time fault state due to some reasons, the load current is I AK1 The jump increases to I AK2 , its power loss will increase significantly and the heat will be serious, causing the radiator temperature to rise significantly. Without considering the feedback mechanism, its operating point in the thermal equilibrium state is (T h6 ,I AK2 ), the heating process can be expressed as (T h4 ,I AK1 ) jumps to (T h4 ,I AK2 ), as the temperature rises to (T h6 ,I AK2 ) operating point, but due to the feedback mechanism in the actual working engineering, the junction to heat sink thermal resistance Z th_jh decreases, so the temperature of the radiator is further reduced. That is, when the load current jumps, the actual steady-state operating point of the system is (T h5 ,I AK2 ), but when the safe operating area is drawn without considering the feedback mechanism, the actual steady-state operating point is (T h5 ,I AK2 ) may fall outside the safe working area, which may cause the staff to misjudge the system instability. The actual working point (T h5 ,I AK2 ) falls outside the safe operating area without considering the feedback mechanism.

Claims

1. A method for drawing a safe operating area for high-voltage and high-power thyristor applications, characterized by: Follow these steps: Step S1: establishing a power loss model of the thyristor under different load currents, gate trigger conditions and different operating frequency parameters, and obtaining the thyristor power loss curve through electric and thermal co-simulation; Step S2: Based on the thermal expansion theory, establish the pressure at both ends of the high-voltage and high-power thyristor under a certain initial installation pressure. F N and radiator temperature T h Functional relationship between F N ( T h ); Step S3: Install the thyristor within the allowable pressure range F N,min < F N < F N,max The thermal resistance Z from the junction to the heat sink of the thyristor is measured at different pressures. th_jh According to the pressure at both ends of the thyristor and the measured junction-to-heat sink thermal resistance under the corresponding conditions, the junction-to-heat sink thermal resistance Z is obtained by data fitting. th_jh and pressure F N The relationship curve of the junction to heat sink thermal resistance and pressure is further obtained as a function of Z th_jh ( F N ), according to the pressure in step S2 F N and radiator temperature T h Functional relationship between F N ( T h ), and finally get the thermal resistance from junction to heat sink Z th_jh and pressure F N and radiator temperature T h Function expression Z th_jh (T h, F N ); Step S4: According to the functional relationship in step S2 F N ( T h ), obtain the initial installation pressure F N_0 The allowable range of the radiator temperature corresponding to the allowable installation pressure range of the thyristor is T h_min < T h < T h_max ; Step S5: Calculating a cooling power curve of the radiator of the high-voltage and high-power thyristor at the corresponding radiator temperature according to the allowable range of the radiator temperature obtained in step S4; Step S6: Obtaining the thyristor limit power loss curve corresponding to the cooling power curve at a certain radiator temperature in step S5 according to the limit thermal balance theory, determining whether there is a tangent point between the thyristor power loss curve and the cooling power curve of the radiator; if not, searching for a power loss curve tangent to the cooling power curve; if so, proceeding to the next step; Step S7: Obtain the radiator temperature according to the intersection of the limit power loss curve and the radiator cooling power curve in step S6 T h And the corresponding operating current of the thyristor I AK , and draw the safe operating area of ​​the thyristor application T h - I AK .

2. The method for drawing a safe operating area for high-voltage and high-power thyristor applications according to claim 1, characterized in that: The power loss model and power loss curve in step S1 are obtained through an electric-thermal joint simulation model.

3. The method for drawing a safe operating area for high-voltage and high-power thyristor applications according to claim 1, characterized in that: The pressure at both ends of the thyristor in step S2 F N and radiator temperature T h Functional relationship between F N ( T h )for: , where k is the coefficient of pressure and heat sink temperature, is the temperature of the radiator, is the initial stress of the thyristor of the converter valve when it is installed, The initial installation pressure is The corresponding radiator temperature.

4. The method for drawing a safe operating area for high-voltage and high-power thyristor applications according to claim 1, characterized in that: The gate trigger conditions in step S1 include trigger current, trigger time and trigger angle.

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