Variable switching frequency junction temperature fluctuation suppression method and device

Abstract

The invention relates to the technical field of power electronic converter control, and discloses a variable switching frequency junction temperature fluctuation suppression method and device, and the method comprises the steps: employing a hysteresis filtering method to calculate a current level, comparing the current level rounding values of a current control period and a previous control period, and combining the hysteresis width judgment, thereby achieving the suppression of the junction temperature fluctuation of the current control period. Current ripples and working condition changes are effectively distinguished; utilizing a pre-established three-dimensional mapping model group; based on the current levels before and after the change of the working condition, determining the optimal switching frequency through the three-dimensional mapping model group by taking the minimum junction temperature fluctuation change as a principle; and carrying out boundary constraint on the optimal switching frequency, and outputting the final switching frequency. Junction temperature fluctuation of the switching device can be effectively suppressed, the reliability of the device is improved, meanwhile, the grid-side current quality is ensured to meet the requirement, and the problem that the switching frequency is frequently changed due to the fact that the device is easily influenced by current ripples in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converter control, and in particular to a method and device for suppressing variable switching frequency junction temperature fluctuations. Background Art

[0002] Single-phase PWM (Pulse Width Modulation) rectifiers, as important power electronic converters, are widely used in renewable energy generation, electric vehicle charging, industrial drives, and other fields. During actual operation, rectifiers must cope with frequent changes in load power. These changes can cause fluctuations in the junction temperature of switching devices, affecting their reliability and service life.

[0003] To suppress junction temperature fluctuations, existing technologies typically employ a fixed switching frequency control strategy. However, this approach has significant technical drawbacks. When load conditions change, the fixed switching frequency cannot be adjusted to the actual operating state, resulting in significant junction temperature fluctuations in the switching device. Especially in applications with high power fluctuations, this junction temperature fluctuation can significantly shorten device lifespan and reduce system reliability.

[0004] Another existing technology solution uses a variable switching frequency control strategy to suppress junction temperature fluctuations. This method maintains a stable device junction temperature by adjusting the switching frequency in real time. However, existing variable switching frequency control methods are susceptible to interference from current ripple. In actual operation, the rectifier's current signal contains both actual current changes caused by changes in load conditions and current ripple generated by switching operations. Existing technologies are unable to effectively distinguish between these two different types of current changes, causing the control system to mistakenly identify current ripple as a change in operating conditions, resulting in unnecessary switching frequency adjustments. This misjudgment not only affects the effectiveness of suppressing junction temperature fluctuations but can also lead to unstable system control.

[0005] Furthermore, existing variable switching frequency control methods often lack a systematic mapping relationship when optimizing switching frequency, making it impossible to accurately predict the junction temperature response characteristics under different current level and switching frequency combinations. This lack of predictive capability makes the selection of switching frequency unscientific and difficult to achieve optimal suppression of junction temperature fluctuations.

[0006] The above-mentioned deficiencies in the prior art result in the single-phase PWM rectifier being unable to effectively suppress junction temperature fluctuations of the switching device when the operating conditions change, thereby affecting the reliability of the system and the service life of the device. Summary of the Invention

[0007] The purpose of the present invention is to provide a method and device for suppressing junction temperature fluctuations with variable switching frequency, aiming to solve the technical problems of large junction temperature fluctuations of switching devices, susceptibility to current ripple, and inaccurate switching frequency adjustment when the operating conditions of a single-phase PWM rectifier change.

[0008] To solve the above technical problems, the present invention provides a method for suppressing junction temperature fluctuations with variable switching frequency, comprising:

[0009] Calculate current levels and distinguish between current ripple and operating condition changes;

[0010] Using a pre-established three-dimensional mapping model group, the three-dimensional mapping model group includes a junction temperature fluctuation mapping model and a current THD (Total Harmonic Distortion) mapping model;

[0011] Based on the current levels before and after the operating condition changes, and with the principle of minimizing the junction temperature fluctuation, the optimal switching frequency is determined by the three-dimensional mapping model group;

[0012] Boundary constraints are performed on the optimal switching frequency, and a final switching frequency is output.

[0013] Optionally, the process of calculating the current level and distinguishing the current ripple and the operating condition change includes:

[0014] Define the current current level rounding value and determine whether the current level of the current control cycle is equal to that of the previous control cycle;

[0015] Distinguish current ripple and operating condition changes by comparing hysteresis loop width;

[0016] The calculation formula for the rounded value of the current level is:

[0017]

[0018] In the formula, round is the rounding function, I gd * is the given current of the system d axis, U gm is the grid side voltage amplitude, U dc * is the DC side voltage reference value, R L is the equivalent load resistance.

[0019] Optionally, the distinguishing between current ripple and operating condition change includes:

[0020] If the current levels are equal, the current levels remain unchanged;

[0021] If the current levels are not equal, the absolute value of the difference is compared with the hysteresis band width to make a judgment:

[0022] When the absolute value of the difference is smaller than the hysteresis band width, it is judged as current ripple and the current level remains unchanged;

[0023] When the absolute value of the difference is greater than or equal to the hysteresis band width, it is judged that the working condition has changed and the current level is updated.

[0024] Optionally, the process of establishing the three-dimensional mapping model group includes:

[0025] Set the ergodic combination of current level and switching frequency within the full power range;

[0026] Combined with the junction temperature calculation model of the rectifier switching device, the junction temperature fluctuation data and grid-side current THD data corresponding to each combination are obtained simultaneously;

[0027] The polynomial fitting method is used to establish three-dimensional mapping models of current level-switching frequency-junction temperature fluctuation and three-dimensional mapping models of current level-switching frequency-current THD.

[0028] Optionally, the polynomial fitting method includes:

[0029] Establish current level I l Junction temperature fluctuation △T j About the switching frequency f s The polynomial fitting parameter k1;

[0030] Establish current level I l When the switching frequency f s About Junction Temperature Fluctuation △T j The polynomial fitting parameter k2.

[0031] Optionally, the process of determining the optimal switching frequency includes:

[0032] Calculating corresponding junction temperature fluctuations using the three-dimensional mapping model group according to the current level and switching frequency before the operating condition changes;

[0033] Determine whether the current level changes before and after the operating condition changes; and

[0034] Switching frequency selection:

[0035] If the current level does not change, the switching frequency remains unchanged;

[0036] If the current level changes, the new switching frequency is inferred through the three-dimensional mapping model group in accordance with the principle of keeping the junction temperature fluctuation to a minimum.

[0037] Optionally, the switching frequency selection is calculated using pre-established polynomial fitting parameters:

[0038] ΔT j (I l(k-1))=ployval(k1(I l (k-1)),f s_update (I l (k-1)));

[0039] f s_opt (I l (k))=ployval(k2(I l (k)),ΔT j (I l (k-1)));

[0040] Among them, △T j is the junction temperature fluctuation, polyval is the polynomial fitting value calculation function, f s_update is the final output switching frequency, f s_opt is the optimal switching frequency k1, k2 are pre-established fitting parameters, k1 represents the current level I l Junction temperature fluctuation △T j About the switching frequency f s The polynomial fitting parameter, k2 represents the current level I l When the switching frequency f s About Junction Temperature Fluctuation △T j The polynomial fitting parameters of .

[0041] Optionally, the process of performing boundary constraints on the optimal switching frequency includes:

[0042] Set the minimum switching frequency boundary and the maximum switching frequency boundary;

[0043] According to the relationship between the optimal switching frequency and the boundary frequency, the final output switching frequency is determined.

[0044] Optionally, using the current THD mapping model, searching for a switching frequency corresponding to when the THD is equal to a preset threshold at the current current level as a minimum switching frequency boundary;

[0045] According to the switch device specification parameters, the maximum switching frequency limit is set;

[0046] If the optimal switching frequency is less than the minimum switching frequency boundary, outputting the minimum switching frequency boundary;

[0047] If the optimal switching frequency is greater than the maximum switching frequency boundary, outputting the maximum switching frequency boundary;

[0048] If the optimal switching frequency is within the boundary range, the optimal switching frequency is output.

[0049] The present invention also provides a device for suppressing junction temperature fluctuations with a variable switching frequency, comprising:

[0050] Current level calculation module, used to calculate current level and distinguish current ripple and operating condition changes;

[0051] A three-dimensional mapping model storage module, used for storing a pre-established three-dimensional mapping model group;

[0052] a switching frequency optimization module for determining an optimal switching frequency using the three-dimensional mapping model group based on the current levels before and after the operating condition changes and with the principle of minimizing the junction temperature fluctuation;

[0053] The switching frequency constraint module is used to perform boundary constraints on the optimal switching frequency and output a final switching frequency.

[0054] Compared with the prior art, the present invention has at least the following beneficial effects:

[0055] By incorporating a hysteresis-filtered current level calculation method, this invention effectively distinguishes current ripple from actual operating condition changes, avoiding misjudgments and frequent switching frequency adjustments caused by current ripple. Furthermore, by employing a three-dimensional mapping model system, a precise mapping relationship between current level, switching frequency, junction temperature fluctuation, and current THD is established. This enables optimized switching frequency control based on the principle of minimizing junction temperature fluctuations, significantly improving the junction temperature stability and control accuracy of single-phase PWM rectifiers under varying operating conditions.

[0056] This invention uses a pre-established and real-time calculation method for polynomial fitting parameters to achieve rapid reverse calculation from junction temperature fluctuations to switching frequency, improving the control system's real-time responsiveness. Furthermore, by setting a minimum switching frequency limit based on the current THD threshold and a maximum switching frequency limit based on device specifications, it ensures that power quality requirements and device safety requirements are met while suppressing junction temperature fluctuations, achieving multi-objective optimal control. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 1. A flow chart of the steps of a method for suppressing junction temperature fluctuations with a variable switching frequency in one embodiment of the present invention;

[0058] Figure 2 This is a flow chart of a current level calculation method based on hysteresis filtering according to an embodiment of the present invention;

[0059] Figure 3 A flow chart for establishing a three-dimensional mapping model according to an embodiment of the present invention;

[0060] Figure 4 A schematic diagram of a three-dimensional mapping model of junction temperature fluctuation, current level, and switching frequency according to an embodiment of the present invention;

[0061] Figure 5 A schematic diagram of a three-dimensional mapping model of THD, current level, and switching frequency according to an embodiment of the present invention;

[0062] Figure 6 Schematic diagram of switching frequency selection for a variable switching frequency strategy according to an embodiment of the present invention Figure 1 ;

[0063] Figure 7 for Figure 6 Schematic diagram of the process of steps 1-3 in FIG;

[0064] Figure 8 A switching frequency selection flow chart of a variable switching frequency strategy according to an embodiment of the present invention;

[0065] Figure 9 A waveform diagram of a current level calculation simulation verification according to an embodiment of the present invention;

[0066] Figure 10 Comparison of the simulated waveforms of the IGBT (Insulated Gate Bipolar Transistor) junction temperature under the fixed frequency and the proposed variable frequency strategies when the load suddenly changes according to one embodiment of the present invention Figure 1 ;

[0067] Figure 11 Comparison of IGBT junction temperature simulation waveforms under fixed frequency and variable frequency strategies when load changes suddenly in one embodiment of the present invention Figure 2 ;

[0068] Figure 12 Comparison of IGBT junction temperature experimental waveforms under a constant frequency strategy when the load suddenly changes according to an embodiment of the present invention Figure 1 ;

[0069] Figure 13 Comparison of IGBT junction temperature experimental waveforms under a constant frequency strategy when the load suddenly changes according to an embodiment of the present invention Figure 2 ;

[0070] Figure 14 Comparison of IGBT junction temperature simulation waveforms under the frequency conversion strategy provided by the present invention when the load suddenly changes according to one embodiment of the present invention Figure 1 ;

[0071] Figure 15 Comparison of IGBT junction temperature simulation waveforms under the frequency conversion strategy provided by the present invention when the load suddenly changes according to one embodiment of the present invention Figure 2 ;

[0072] Figure 16 This is a topology diagram of a single-phase PWM rectifier in one embodiment of the present invention. DETAILED DESCRIPTION

[0073] The following, in conjunction with a schematic diagram, provides a more detailed description of a method and apparatus for suppressing junction temperature fluctuations in a variable switching frequency system. These schematic diagrams illustrate preferred embodiments of the present invention. It should be understood that those skilled in the art may modify the present invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as a general guideline for those skilled in the art and not as a limitation of the present invention.

[0074] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description and claims. It should be noted that the drawings are greatly simplified and not to exact scale, and are provided solely for the purpose of assisting in the description of the embodiments of the present invention.

[0075] The present invention provides a method and device for suppressing junction temperature fluctuations of variable switching frequency. Figure 1 , including the following steps:

[0076] S1. Calculate the current level and distinguish between current ripple and operating condition changes;

[0077] S2. Using a pre-established three-dimensional mapping model group, the three-dimensional mapping model group includes a junction temperature fluctuation mapping model and a current THD mapping model;

[0078] S3. Based on the current levels before and after the operating condition changes, and with the principle of minimizing the junction temperature fluctuation, determine the optimal switching frequency using the three-dimensional mapping model group;

[0079] S4. Perform boundary constraints on the optimal switching frequency and output a final switching frequency.

[0080] This embodiment provides a method for suppressing junction temperature fluctuations with a variable switching frequency. The method calculates the current level through hysteresis filtering and optimizes the switching frequency using a three-dimensional mapping model group, thereby effectively suppressing junction temperature fluctuations and improving the reliability and efficiency of the rectifier.

[0081] In step S1 , the current level calculation adopts a hysteresis filtering method, which can effectively distinguish between current ripple and actual operating condition changes, and avoids the problem of frequent adjustment of switching frequency due to current ripple in traditional methods.

[0082] Specifically, please refer to Figure 2 The process of calculating the current level and distinguishing the current ripple and the operating condition change includes:

[0083] First, define the current current level rounding value and determine the current level I of the current control cycle. V (k) and the current level I of the previous control cycle V (k-1) are equal.

[0084] The calculation formula for the rounded value of the current level is:

[0085]

[0086] In the formula, round is the rounding function, I gd * is the given current of the system d axis, U gm is the grid side voltage amplitude, U dc * is the DC side voltage reference value, R L is the equivalent load resistance.

[0087] Then, the current ripple and operating condition changes are distinguished by comparing the hysteresis loop width.

[0088] The distinguishing between current ripple and operating condition changes includes:

[0089] If the current levels are equal, that is, I V (k)=I V (k-1), it is judged as current ripple, and the current level remains unchanged, that is, I l (k)=I l (k-1);

[0090] If the current levels are not equal, that is, I V (k)≠I V (k-1), judge by comparing the absolute value of the difference with the hysteresis band width:

[0091] When the absolute value of the difference is less than the hysteresis band width, that is, |I V (k)-I V (k-1)| lim , it is judged as current ripple, and the current level remains unchanged, that is, I l (k)=I l (k-1).

[0092] When the absolute value of the difference is greater than or equal to the hysteresis band width, that is, |I V (k)-I V (k-1|≥I lim , it is judged that the working condition has changed, and the current level is updated to I l (k) = I V (k).

[0093] In a specific example, the hysteresis loop width I lim It can be set to a value between 0.5-2, and the specific value can be adjusted according to the system's current ripple level and response speed requirements.

[0094] ​In this embodiment, the hysteresis filtering method is used to effectively distinguish between current ripple and operating condition changes, avoid frequent and ineffective adjustment of the switching frequency, and improve the stability of the control system.

[0095] In step S2, the three-dimensional mapping model group includes a junction temperature fluctuation mapping model and a current THD mapping model, which provides an accurate data basis for subsequent switching frequency optimization.

[0096] like Figure 3 As shown, the process of establishing the three-dimensional mapping model group includes:

[0097] First, set the current level I within the full power range l With the switching frequency f s The traversal combination of .

[0098] In a specific example, the current level range can be set to 5-40, the switching frequency range can be set to 5 kHz-20 kHz, and the traversal step sizes are 5 and 0.5 kHz respectively.

[0099] Then, combined with the junction temperature calculation model of the rectifier switching device, the junction temperature fluctuation data △T corresponding to each combination is obtained at the same time. j And grid-side current THD data.

[0100] The junction temperature calculation model is a common method used by those skilled in the art and can be modeled using a Foster Network Model (Foster Network Model) or a Cauer Network Model (Cauer Network Model), which will not be described in detail.

[0101] Finally, the polynomial fitting method is used to establish the three-dimensional mapping models of current level-switching frequency-junction temperature fluctuation and the three-dimensional mapping models of current level-switching frequency-current THD respectively.

[0102] The polynomial fitting may adopt a second-order or third-order polynomial, and the specific order may be determined according to the fitting accuracy requirement.

[0103] In this embodiment, an accurate mathematical mapping relationship between the current level, switching frequency, junction temperature fluctuation, and current THD is established, providing a theoretical basis for real-time optimization control.

[0104] In step S3, based on the current levels before and after the operating condition changes and with the principle of minimizing the junction temperature fluctuation, the optimal switching frequency is determined by the three-dimensional mapping model group, thereby achieving active suppression of the junction temperature fluctuation.

[0105] Further, Figure 4-Figure 5 The visualization results of the three-dimensional mapping model are shown respectively. Specifically, Figure 4 Shows the junction temperature fluctuation ΔT at each current level j_T1 Regarding the fitting curve of the switching frequency, the junction temperature fluctuation is positively correlated with the current level and the switching frequency. Figure 5 The fitting curves of current THD with respect to switching frequency at various current levels are shown, that is, current THD is negatively correlated with both current level and switching frequency.

[0106] like Figure 6-Figure 8 As shown, the process of determining the optimal switching frequency includes:

[0107] First, according to the current level I before the working condition changes l (k-1) and switching frequency f s_update (I l (k-1)), using the junction temperature fluctuation mapping model in the three-dimensional mapping model group to calculate the corresponding junction temperature fluctuation ΔT j (I l (k-1)).

[0108] Then, determine whether the current level changes before and after the working condition changes, that is, compare I l (k) and I l The value of (k-1).

[0109] Next, select the switching frequency:

[0110] If the current level does not change, that is, I l (k) = I l (k-1), the switching frequency remains unchanged, that is:

[0111] f s_opt (I l (k))=f s_update (I l (k-1));

[0112] If the current level changes, that is, I l (k)≠I l (k-1), based on the principle of keeping the junction temperature fluctuation to a minimum, the new switching frequency is inferred through the three-dimensional mapping model group.

[0113] The switching frequency selection is calculated using pre-established polynomial fitting parameters:

[0114] ΔT j (I l (k-1))=ployval(k1(I l (k-1)),f s_update (I l (k-1)));

[0115] f s_opt(I l (k))=ployval(k2(I l (k)),ΔT j (I l (k-1)));

[0116] Among them, △T j is the junction temperature fluctuation, polyval is the polynomial fitting value calculation function, f s_update is the final output switching frequency, f s_opt is the optimal switching frequency k1, k2 are pre-established fitting parameters, k1 represents the current level I l Junction temperature fluctuation △T j About the switching frequency f s The polynomial fitting parameter, k2 represents the current level I l When the switching frequency f s About Junction Temperature Fluctuation △T j The polynomial fitting parameters of .

[0117] In this embodiment, the optimal switching frequency is determined by keeping the junction temperature fluctuation to a minimum, thereby effectively suppressing the junction temperature fluctuation caused by the change in working conditions and extending the service life of the switching device.

[0118] In step S4, boundary constraints are applied to the optimal switching frequency, and a final switching frequency is output, thereby ensuring safe and reliable operation of the rectifier under various working conditions.

[0119] Specifically, the process of performing boundary constraints on the optimal switching frequency includes:

[0120] First, set the minimum switching frequency boundary and the maximum switching frequency boundary.

[0121] The boundary setting takes into account the constraints of both current quality and device safety.

[0122] Specifically, the current THD mapping model is used to find the switching frequency corresponding to the time when the THD is equal to the preset threshold value at the current current level as the minimum switching frequency boundary f s_min (I l (k)).

[0123] In a specific example, the preset threshold is 5%, which meets the requirements of the power grid harmonic standard.

[0124] According to the switch device specifications, set the maximum switching frequency limit f s_max .

[0125] The switch device specification parameters include but are not limited to maximum switching frequency, power loss characteristic curve, etc., which are common means used by those skilled in the art and will not be described in detail.

[0126] Then, according to the relationship between the optimal switching frequency and the boundary frequency, the final output switching frequency is determined:

[0127]

[0128] Specifically, if the optimal switching frequency is less than the minimum switching frequency limit, that is, f s_opt (I l (k)) <f s_min (I l (k)), then the minimum switching frequency boundary is output, i.e. f s_update =f s_min (I l (k));

[0129] If the optimal switching frequency is greater than the maximum switching frequency limit, that is, f s_opt (I l (k))>f s_max , then the maximum switching frequency boundary is output, i.e. f s_update =f s_max ;

[0130] If the optimal switching frequency is within the boundary range, that is, f s_min (I l (k))≤f s_opt (I l (k))≤f s_max , then the optimal switching frequency is output, i.e. f s_update =f s_opt (I l (k)).

[0131] In a specific example, for an IGBT device, the maximum switching frequency limit is generally set to 20 kHz-50 kHz, and the specific value can be determined according to the device model and heat dissipation conditions.

[0132] In this embodiment, the switching frequency is ensured to be within a safe and feasible range through boundary constraints, which not only ensures the current quality requirements but also avoids device overload, thereby improving the reliability of the system.

[0133] For further information, please refer to Figure 9 , Figure 9 Shows the load R L When the current level suddenly changes from 20Ω to 10Ω, that is, from 20 to 40, the system d-axis given current I gd *With current level I l The waveform of Figure 9 It can be seen that the current level calculation method proposed in this application can effectively track I gd*Changes with high accuracy. The current level calculation method in the aforementioned step S1 can be verified.

[0134] Furthermore, based on the above-mentioned strategy content, this embodiment also proposes a comparative study of simulation verification and experimental verification to verify the effectiveness of the suppression strategy proposed in this application in suppressing the junction temperature fluctuation of the PWM rectifier power device under different load mutation conditions. By comparing the performance of the fixed-frequency control strategy and the suppression strategy of this application in terms of device T1 junction temperature changes, the practical application effect of the proposed method was evaluated. Specifically:

[0135] Figure 10 The simulation shows the junction temperature change of device T1 in the single-phase PWM rectifier. L The junction temperature changes under the fixed frequency control strategy and the suppression strategy proposed in this application before and after the sudden change from 20Ω to 10Ω; Figure 10 It can be seen that when the suppression strategy proposed in this application is adopted, the low-frequency junction temperature fluctuation is significantly reduced from 35.98°C to 13.14°C.

[0136] Figure 11 The simulation shows the junction temperature change of device T1 in the single-phase PWM rectifier. L The junction temperature changes under the fixed frequency control strategy and the suppression strategy proposed in this application before and after the sudden change from 10Ω to 20Ω; Figure 11 It can be seen that when the suppression strategy proposed in this application is adopted, the low-frequency junction temperature fluctuation is significantly reduced from 36.00°C to 14.40°C.

[0137] Figure 12-15 The load R under the experiment is shown respectively. L Schematic diagram showing the changes in DC voltage, d-axis current set value, and current level before and after the mutation, as well as a comparison of the junction temperature of the T1 device using the fixed-frequency control strategy and the suppression strategy proposed in this application.

[0138] Specifically, Figure 12 Shows the load R L The junction temperature changes before and after the change from 25Ω to 20Ω using the fixed frequency control strategy are shown in the figure below. Figure 12 It can be seen that when the fixed-frequency control strategy is adopted, the low-frequency junction temperature fluctuation is 11.3°C.

[0139] Figure 13 Shows the load R L The junction temperature changes before and after the change from 20Ω to 25Ω using the fixed frequency control strategy are shown in the figure below. Figure 13 It can be seen that when the fixed-frequency control strategy is adopted, the low-frequency junction temperature fluctuation is 11.1°C.

[0140] Figure 14 Shows the load R LThe junction temperature changes before and after the sudden change from 25Ω to 20Ω using the suppression strategy proposed in this application are shown in the figure. Figure 14 It can be seen that when the suppression strategy proposed in this application is adopted, the low-frequency junction temperature fluctuation is 8.9°C, which is lower than that of the fixed-frequency control strategy.

[0141] Figure 15 Shows the load R L The junction temperature changes using the suppression strategy proposed in this application before and after the sudden change from 20Ω to 25Ω. When the suppression strategy proposed in this application is used, the low-frequency junction temperature fluctuation is 9.4°C, which is lower than that of the fixed-frequency control strategy.

[0142] Based on the above simulation and experimental results, it can be seen that the suppression strategy proposed in this application has a significant effect in reducing the junction temperature fluctuation of the PWM rectifier power device. Or a relatively small load change under experimental conditions The proposed suppression strategies can effectively suppress the low-frequency junction temperature fluctuation of device T1, achieving significant performance improvement compared with the traditional fixed-frequency control strategy.

[0143] In summary, the method for suppressing junction temperature fluctuations with variable switching frequency provided by the embodiment of the present invention has the following beneficial effects:

[0144] The hysteresis filtering method is used to effectively distinguish current ripple from operating condition changes, avoiding frequent and ineffective adjustments of the switching frequency and improving the stability of the control system. An accurate three-dimensional mapping model group is established to achieve accurate mapping between junction temperature fluctuations and switching frequency, providing a theoretical basis for optimized control. The optimization principle of minimizing junction temperature fluctuations is adopted to effectively suppress junction temperature fluctuations caused by operating condition changes and extend the service life of the switching device. Boundary constraints are used to ensure that the switching frequency is within a safe and feasible range, which not only meets the current quality requirements but also ensures the safe operation of the device. The overall method is simple to implement, has a small amount of calculation, is suitable for real-time control applications, and has good engineering practicality.

[0145] Example 2

[0146] An embodiment of the present invention provides a device for suppressing junction temperature fluctuations with a variable switching frequency, which can realize the hardware implementation of the method described in the first embodiment.

[0147] The variable switching frequency junction temperature fluctuation suppression device includes: a current level calculation module, a three-dimensional mapping model storage module, a switching frequency optimization module and a switching frequency constraint module.

[0148] The current level calculation module is used to calculate the current level and distinguish between current ripple and operating condition changes.

[0149] The current level calculation module includes a current level rounding unit, a hysteresis band comparison unit and a current level output unit.

[0150] The current level rounding unit is used to calculate the current level rounding value I according to the instantaneous value of the current grid side voltage V (k); The hysteresis comparison unit is used to compare the current level difference between the current control cycle and the previous control cycle and the hysteresis loop width; The current level output unit is used to determine the final current level I according to the hysteresis comparison result l (k).

[0151] The three-dimensional mapping model storage module is used to store a pre-established three-dimensional mapping model group, where the three-dimensional mapping model group includes a junction temperature fluctuation mapping model and a current THD mapping model.

[0152] The three-dimensional mapping model storage module stores polynomial fitting parameters, including current level I l Junction temperature fluctuation △T j About the switching frequency f s The fitting parameter k1, and the current level I l When the switching frequency f s About Junction Temperature Fluctuation △T j The fitting parameter k2.

[0153] In a specific example, the three-dimensional mapping model storage module can be implemented using EEPROM or Flash memory, which has a power-off retention function to ensure reliable storage of mapping parameters.

[0154] The switching frequency optimization module is used to determine the optimal switching frequency through the three-dimensional mapping model group based on the current level before and after the working condition changes and with the principle of minimizing the junction temperature fluctuation.

[0155] The switching frequency optimization module has a built-in polyval calculation unit for performing polynomial fitting value calculation; it also includes a current level change judgment unit and a switching frequency selection unit, which are respectively used to judge working condition changes and select a suitable switching frequency.

[0156] The switching frequency constraint module is used to perform boundary constraints on the optimal switching frequency and output a final switching frequency.

[0157] The switching frequency constraint module includes a minimum frequency constraint unit, a maximum frequency constraint unit and a frequency selection unit.

[0158] The minimum frequency constraint unit sets the minimum switching frequency boundary based on the current THD mapping model; the maximum frequency constraint unit sets the maximum switching frequency boundary based on the device safety parameter; and the frequency selection unit determines the final output frequency according to the relationship between the optimal switching frequency and the boundary frequency.

[0159] In a specific example, the modules are connected via a data bus, and data transmission adopts serial communication or parallel communication. The specific communication protocol belongs to the common means used by those skilled in the art and will not be described in detail.

[0160] In a specific example, the apparatus may further include a parameter updating module for updating the three-dimensional mapping model parameters online to adapt to the effects of device aging and environmental changes.

[0161] In a specific example, the device may further include a fault detection module, configured to monitor abnormal conditions during the switching frequency adjustment process, and switch to a safe mode of operation when an abnormality is detected.

[0162] In a specific example, the device can be integrated into a single-phase PWM rectifier system. Figure 16 The single-phase PWM rectifier topology diagram is shown. The single-phase PWM rectifier main circuit adopts a single-phase two-level PWM rectifier topology, including input inductors, switching devices, freewheeling diodes, DC side capacitors, etc. The variable switching frequency junction temperature fluctuation suppression device is connected to the single-phase PWM rectifier main circuit via a control signal line and outputs a switching frequency control signal f in real time. s_update , adjusting the switching frequency of the switching device to achieve active suppression of junction temperature fluctuations.

[0163] The variable switching frequency junction temperature fluctuation suppression device provided by the embodiment of the present invention has the following beneficial effects:

[0164] The modular design has a clear structure and clear responsibilities for each functional module, facilitating hardware implementation and software development. It has comprehensive boundary constraint functions to ensure the safety and reliability of the output switching frequency. It supports online parameter updates and fault detection, improving the system's adaptability and reliability. Its overall structure is compact and the cost is low, making it suitable for industrial applications.

[0165] In summary, the present invention proposes a current level calculation method based on hysteresis filtering and a switching frequency optimization strategy based on a three-dimensional mapping model. The hysteresis filtering method effectively solves the technical problem of frequent adjustment of the switching frequency caused by current ripple interference in traditional methods; the three-dimensional mapping model establishes a precise mathematical relationship between the current level, switching frequency and junction temperature fluctuation, and realizes the active prediction and suppression of junction temperature fluctuation. The device realizes the hardware of the method through modular design, and each functional module has a clear division of labor and coordinated work, providing reliable hardware support for the engineering implementation of the method. The present invention realizes the intelligent suppression of junction temperature fluctuations of single-phase PWM rectifiers, effectively solves the problem of large low-frequency junction temperature fluctuations of switching devices caused by complex working conditions or frequent changes in output power of single-phase PWM rectifiers, significantly improves the reliability, efficiency and service life of the rectifier, and has important theoretical significance and practical value.

[0166] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for suppressing junction temperature fluctuations in a variable switching frequency, characterized in that: include: Calculate current levels and distinguish between current ripple and operating condition changes; Using a pre-established three-dimensional mapping model group, the three-dimensional mapping model group includes a junction temperature fluctuation mapping model and a current THD mapping model; Based on the current levels before and after the operating condition changes, and with the principle of minimizing the junction temperature fluctuation, the optimal switching frequency is determined by the three-dimensional mapping model group; Boundary constraints are performed on the optimal switching frequency, and a final switching frequency is output.

2. The method for suppressing junction temperature fluctuations with variable switching frequency according to claim 1, characterized in that: The process of calculating the current level and distinguishing the current ripple and the operating condition change includes: Define the current current level rounding value and determine whether the current level of the current control cycle is equal to that of the previous control cycle; Distinguish current ripple and operating condition changes by comparing hysteresis loop width; The calculation formula for the rounded value of the current level is: In the formula, round is the rounding function, I gd * is the given current of the system d axis, U gm is the grid side voltage amplitude, U dc * is the DC side voltage reference value, R L is the equivalent load resistance.

3. The method for suppressing junction temperature fluctuations with variable switching frequency according to claim 2, characterized in that: The distinguishing between current ripple and operating condition changes includes: If the current levels are equal, the current levels remain unchanged; If the current levels are not equal, the absolute value of the difference is compared with the hysteresis band width to make a judgment: When the absolute value of the difference is smaller than the hysteresis band width, it is judged as current ripple and the current level remains unchanged; When the absolute value of the difference is greater than or equal to the hysteresis band width, it is judged that the working condition has changed and the current level is updated.

4. The method for suppressing junction temperature fluctuations with variable switching frequency according to claim 1, wherein: The process of establishing the three-dimensional mapping model group includes: Set the ergodic combination of current level and switching frequency within the full power range; Combined with the junction temperature calculation model of the rectifier switching device, the junction temperature fluctuation data and grid-side current THD data corresponding to each combination are obtained simultaneously; The polynomial fitting method is used to establish three-dimensional mapping models of current level-switching frequency-junction temperature fluctuation and three-dimensional mapping models of current level-switching frequency-current THD.

5. The method for suppressing junction temperature fluctuations with variable switching frequency according to claim 4, characterized in that: The polynomial fitting method comprises: Establish current level I l Junction temperature fluctuation △T j About the switching frequency f s The polynomial fitting parameter k1; Establish current level I l When the switching frequency f s About Junction Temperature Fluctuation △T j The polynomial fitting parameter k2.

6. The method for suppressing junction temperature fluctuations with variable switching frequency according to claim 1, characterized in that: The process of determining the optimal switching frequency includes: Calculating corresponding junction temperature fluctuations using the three-dimensional mapping model group according to the current level and switching frequency before the operating condition changes; Determine whether the current level changes before and after the operating condition changes; and Switching frequency selection: If the current level does not change, the switching frequency remains unchanged; If the current level changes, the new switching frequency is inferred through the three-dimensional mapping model group in accordance with the principle of keeping the junction temperature fluctuation to a minimum.

7. The method for suppressing junction temperature fluctuations with variable switching frequency according to claim 6, characterized in that: The switching frequency selection is calculated using pre-established polynomial fitting parameters: ΔT j (I l (k-1))=ployval(k1(I l (k-1)),f s_updae (I l (k-1))); f s_opt (I l (k))=ployval(k2(I l (k)),ΔT j (I l (k-1))); Among them, △T j is the junction temperature fluctuation, polyval is the polynomial fitting value calculation function, f s_update is the final output switching frequency, f s_opt is the optimal switching frequency, k1 and k2 are pre-established fitting parameters, k1 represents the current level I l Junction temperature fluctuation △T j About the switching frequency f s The polynomial fitting parameter, k2 represents the current level I l When the switching frequency f s About Junction Temperature Fluctuation △T j The polynomial fitting parameters of .

8. The method for suppressing junction temperature fluctuations with variable switching frequency according to claim 1, characterized in that: The process of performing boundary constraints on the optimal switching frequency includes: Set the minimum switching frequency boundary and the maximum switching frequency boundary; According to the relationship between the optimal switching frequency and the boundary frequency, the final output switching frequency is determined.

9. The method for suppressing junction temperature fluctuations with variable switching frequency according to claim 8, characterized in that: Using the current switching frequency THD mapping model, find the switching frequency corresponding to when the THD is equal to the preset threshold at the current current level as the minimum switching frequency boundary; According to the switch device specification parameters, the maximum switching frequency limit is set; If the optimal switching frequency is less than the minimum switching frequency boundary, outputting the minimum switching frequency boundary; If the optimal switching frequency is greater than the maximum switching frequency boundary, outputting the maximum switching frequency boundary; If the optimal switching frequency is within the boundary range, the optimal switching frequency is output.

10. A device for suppressing junction temperature fluctuations with a variable switching frequency, characterized in that: include: Current level calculation module, used to calculate current level and distinguish current ripple and operating condition changes; A three-dimensional mapping model storage module, used for storing a pre-established three-dimensional mapping model group; a switching frequency optimization module for determining an optimal switching frequency using the three-dimensional mapping model group based on the current levels before and after the operating condition changes and with the principle of minimizing the junction temperature fluctuation; The switching frequency constraint module is used to perform boundary constraints on the optimal switching frequency and output a final switching frequency.

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