DC microgrid parallel DC / DC converter IGBT temperature control method

Abstract

This invention discloses a method for IGBT temperature equalization control in parallel DC / DC converters of DC microgrids, belonging to the field of IGBT active temperature equalization control technology. The method includes nine steps: IGBT power loss calculation, IGBT thermal network model establishment, IGBT thermoelectric coupling model construction, IGBT junction temperature calculation in the DC / DC converter, average IGBT junction temperature calculation in the parallel DC / DC converter, calculation of the difference between the IGBT junction temperature and the average junction temperature in the parallel DC / DC converter, calculation of the virtual impedance for IGBT temperature equalization fine-tuning, adding the virtual impedance to the droop control loop, and generating PWM drive signals for the parallel DC / DC converter based on voltage and current dual closed-loop control. This invention adds the virtual impedance for IGBT temperature equalization fine-tuning to the traditional droop control, adjusting the current flowing through the IGBTs in each DC / DC converter, so that the IGBT junction temperatures in each parallel DC / DC converter tend to be uniform, thereby improving the overall system reliability.

Description

Technical Field

[0001] This invention belongs to the field of IGBT active temperature equalization control technology, and specifically relates to a method for temperature equalization control of IGBTs in a parallel DC / DC converter of a DC microgrid. Background Technology

[0002] Against the backdrop of "carbon peaking and carbon neutrality," vigorously developing renewable energy and transitioning energy production to renewable energy is a major requirement for the sustainable development of energy and the economy in China and even globally. Microgrids, as an effective carrier of distributed power sources, can support the main power grid and, with their flexible operating modes and controllability, have become a solution for the large-scale development and utilization of renewable energy. Microgrids are generally divided into DC microgrids and AC microgrids. Compared to AC microgrids, DC microgrids reduce the number of converters and power conversion stages, and also do not have problems such as phase synchronization, reactive power flow, and harmonics, making them easier to control and thus attracting widespread attention and research.

[0003] When a DC microgrid is operating stably, without considering the differences in IGBT parameters and the influence of line resistance in the parallel DC / DC converter circuit, the junction temperatures of each IGBT will tend to be uniform. However, if the influence of line resistance is considered, under traditional droop control, the current flowing through each IGBT in the parallel DC / DC converter circuit will differ, resulting in varying thermal stresses on each IGBT. This can cause some modules with higher thermal stress to fail before others, reducing the overall reliability of the converter. Furthermore, due to manufacturing process errors and human factors during installation, there are differences in the electrothermal parameters between the converter modules. Even with uniform current or power distribution, the thermal stress of each IGBT will still differ. Therefore, traditional droop control has certain limitations in achieving uniform IGBT temperature in parallel DC / DC converter circuits.

[0004] To address the existing problems, this invention proposes a method for temperature equalization control of IGBTs in parallel DC / DC converters in a DC microgrid. By adding a virtual impedance for temperature equalization fine-tuning to the traditional droop control, the current flowing through the IGBTs in each DC / DC converter is adjusted, so that the junction temperature of the IGBTs in each parallel DC / DC converter tends to be uniform, thereby improving the overall power supply reliability of the DC microgrid. Summary of the Invention

[0005] The purpose of this invention is to propose a method for temperature control of IGBTs in parallel DC / DC converters in DC microgrids.

[0006] The aforementioned method for controlling the uniform temperature of IGBTs in parallel DC / DC converters in a DC microgrid mainly includes the following steps:

[0007] S1. IGBT power loss calculation;

[0008] S2. Establishment of IGBT thermal network model;

[0009] S3. IGBT thermoelectric coupling model construction;

[0010] S4. Calculation of IGBT junction temperature in DC / DC converter;

[0011] S5. Calculation of average IGBT junction temperature of parallel DC / DC converters;

[0012] S6. Calculation of the difference between the IGBT junction temperature and the average IGBT junction temperature of a parallel DC / DC converter;

[0013] S7. Calculation of virtual impedance for IGBT temperature-controlled fine-tuning;

[0014] S8. Add the virtual impedance of IGBT temperature equalization fine-tuning to the droop control loop;

[0015] S9. Generate PWM drive signal for parallel DC / DC converter based on voltage and current dual closed-loop control.

[0016] This invention proposes a method for temperature control of IGBTs in parallel DC / DC converters of DC microgrids. The calculation process for IGBT power loss is as follows:

[0017] IGBT power losses are divided into conduction losses, switching losses, and drive losses. IGBT drive losses account for less than 0.1%, and their impact on IGBT junction temperature calculations can be ignored. IGBT conduction losses are closely related to the IGBT's on-state voltage, the bridge arm current flowing through the IGBT, the IGBT junction temperature, and the duty cycle.

[0018]

[0019] In the formula, V ce This is the IGBT turn-on voltage, and its value is related to the IGBT current and the IGBT junction temperature; a (t) represents the current flowing through the IGBT; T j (t) represents the IGBT junction temperature; δ(t) represents the duty cycle;

[0020] IGBT switching losses are closely related to the current flowing through the IGBT, the DC-side voltage, the IGBT junction temperature, and the IGBT switching frequency.

[0021]

[0022] In the formula, E on+off This is the sum of the IGBT turn-on and turn-off losses; f sw U is the IGBT switching frequency; dc K is the DC bus voltage. vU is the DC voltage coefficient; ref This is the DC-side reference voltage.

[0023] This invention proposes a method for temperature control of IGBTs in parallel DC / DC converters of DC microgrids. The IGBT thermal network model is established based on the following: when current flows through the IGBT, the IGBT generates a certain amount of heat, and the heat transfer inside the IGBT is mainly through thermal conduction. The heat transfer occurs differently in different layers of the IGBT, requiring separate thermal modeling for each layer to obtain a one-dimensional equivalent thermal network model inside the IGBT. Figure 1 As shown.

[0024] This invention proposes a method for temperature control of IGBTs in parallel DC / DC converters in DC microgrids. The IGBT thermoelectric coupling model is built, and the IGBT junction temperature is calculated based on the IGBT power loss and the IGBT thermal network model.

[0025] This invention proposes a method for temperature control of IGBTs in parallel DC / DC converters of DC microgrids, wherein the IGBT junction temperature calculation expression is:

[0026]

[0027] In the formula, T j T represents the junction temperature of the IGBT. a Ambient temperature; Z represents the electrical losses of the IGBT and the anti-parallel diode. ha This refers to the thermal resistance of the IGBT.

[0028] This invention proposes a method for controlling the average temperature of IGBTs in parallel DC / DC converters in a DC microgrid, and the formula for calculating the average junction temperature of the parallel IGBTs is provided.

[0029]

[0030] In the formula, T IGBT_i Let be the junction temperature of the IGBT in the i-th parallel DC / DC converter.

[0031] This invention proposes a method for controlling the uniform temperature of IGBTs in parallel DC / DC converters in DC microgrids, wherein the difference between the junction temperature of the IGBTs in the parallel DC / DC converters and the average junction temperature of the IGBTs is specified.

[0032] ΔT IGBT_i =T IGBT_i -T IGBT_ave

[0033] This invention proposes a method for IGBT temperature equalization control in parallel DC / DC converters of a DC microgrid. The virtual impedance for fine-tuning the parallel IGBT temperature equalization is calculated as follows: based on the difference between the junction temperature of the IGBTs in each parallel DC / DC converter and the average junction temperature, the virtual impedance for fine-tuning the IGBT temperature equalization is obtained via a PI controller output. When the junction temperature of the IGBTs in each parallel DC / DC converter equals the average junction temperature of the IGBTs, the purpose of IGBT temperature equalization control is achieved.

[0034]

[0035] In the formula, T IGBT_i k is the junction temperature of the IGBT in the i-th parallel DC / DC circuit; i k p These are the coefficients of the integral and proportional elements of the PI controller.

[0036] This invention proposes a method for temperature control of IGBTs in parallel DC / DC converters of DC microgrids. The method involves adding the virtual impedance for IGBT temperature adjustment to the droop control loop. The IGBT junction temperature is related to the ambient temperature, IGBT switching frequency, current flowing through the IGBT, IGBT on-state voltage, and duty cycle.

[0037] When the ambient temperature, IGBT switching frequency, and duty cycle are fixed, the IGBT turn-on voltage is a function of the IGBT current. Therefore, the IGBT junction temperature is only related to the IGBT current. The IGBT junction temperature distribution can be changed by changing the IGBT current. By adding a temperature equalization and fine-tuning virtual impedance to the traditional droop control loop, the current flowing through the IGBTs in each DC / DC converter can be adjusted, so that the IGBT junction temperatures in each parallel DC / DC converter tend to be consistent, thereby improving the overall system reliability.

[0038] V o_i =V ref -(R V_i +R IGBT_i )I o_i

[0039] In the formula, R IGBT_i This is the virtual impedance for temperature equalization and fine-tuning of the i-th IGBT.

[0040] This invention proposes a method for temperature control of IGBTs in parallel DC / DC converters in DC microgrids, which generates PWM drive signals for parallel DC / DC converters based on voltage and current dual closed-loop control. Attached Figure Description

[0041] Figure 1 This is an IGBT thermal network model.

[0042] Figure 2 This is a thermoelectric coupling model for IGBTs.

[0043] Figure 3 This is a diagram of a dual closed-loop control structure for voltage and current.

[0044] Figure 4 This is a simulation structure for a DC microgrid.

[0045] Figure 5 To consider the junction temperature of IGBTs in a parallel DC / DC circuit when line resistance is taken into account.

[0046] Figure 6 The current in a parallel DC / DC circuit when considering line resistance. Detailed Implementation

[0047] The technical solution of the present invention will be further described in detail below with reference to specific examples. Obviously, the embodiments described herein are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0048] A method for temperature control of IGBTs in parallel DC / DC converters in a DC microgrid is proposed. A simulation of a parallel DC / DC converter in a DC microgrid is built using MATLAB / Simulink and PLECS Blockset. The simulation model consists of three parallel distributed power sources and a DC load, such as... Figure 4 As shown.

[0049] The IGBT module used in the simulation is the Infineon FF50R12RT4. Considering the influence of manufacturing process errors and human factors during installation, which lead to differences in the electrothermal parameters between the various converter modules, this invention generates two sets of random thermal network parameters according to a normal distribution. The normal distribution uses the factory parameters as the mean and generates random numbers with a variance of 0.05 times the factory parameters.

[0050] Set the output line resistance of the DC / DC converter to R respectively. linel =0.1Ω, R line2 =0.15Ω, R line3 =0.2Ω. The bus voltage reference value is set to 400V, the IGBT switching frequency is set to 8000Hz, and the ambient temperature is set to 25℃. The simulation duration is set to 100s. Traditional droop control is used before 15s, and the active temperature equalization control strategy of the DC microgrid IGBT proposed in this invention is used after 15s. The current and IGBT junction temperature in the three parallel DC / DC circuits are as follows: Figure 5 , 6As shown, under the traditional droop control strategy, considering the different line resistances, the currents in the three parallel DC / DC circuits differ, leading to uneven junction temperatures of the three IGBTs. Under the active temperature equalization control strategy for IGBTs in a DC microgrid, the currents in the three parallel DC / DC circuits are distributed according to the IGBT junction temperatures. The current in the DC / DC converter circuit with the higher IGBT junction temperature gradually decreases, while the current in the DC / DC converter circuit with the lower IGBT junction temperature gradually increases. Eventually, the junction temperatures of the three IGBTs gradually converge, thus achieving IGBT junction temperature equalization even when there are differences in line resistance.

[0051] As described above, the present invention has been described in detail. Obviously, the present invention is not limited to the given embodiments. Any modifications that can be made by those skilled in the art without substantially departing from the inventive point and effect of the present invention are also included within the protection scope of the present invention.

Claims

1. A method for temperature control of IGBTs in parallel DC / DC converters in a DC microgrid, characterized in that, This method mainly includes the following steps: S1. IGBT power loss calculation; S2. Establishment of IGBT thermal network model; S3. Construction of IGBT thermoelectric coupling model; S4. Calculation of IGBT junction temperature in DC / DC converter; S5. Calculation of average IGBT junction temperature of parallel DC / DC converters; S6. Calculation of the difference between the IGBT junction temperature and the average IGBT junction temperature of a parallel DC / DC converter; S7. Calculation of virtual impedance for IGBT temperature-controlled fine-tuning; Based on the difference between the IGBT junction temperature and the average junction temperature in each parallel DC / DC converter, the virtual impedance for IGBT temperature equalization is obtained via the output of the PI controller. When the IGBT junction temperature in each parallel DC / DC converter equals the average junction temperature, the IGBT temperature equalization control is achieved. In the formula, T j_i is the IGBT junction temperature in the i-th parallel DC / DC circuit; k i , k p is the coefficient of the integral and proportional links of the PI controller; R IGBT_i is the i-th IGBT temperature equalization fine-tuning virtual impedance; S8. Add the virtual impedance of IGBT temperature equalization fine-tuning to the droop control loop; The virtual impedance for IGBT temperature equalization and fine adjustment is added to the droop control loop. The IGBT junction temperature is related to the ambient temperature, IGBT switching frequency, IGBT current, IGBT on-state voltage, and duty cycle. When the ambient temperature, IGBT switching frequency, and duty cycle are fixed, the IGBT turn-on voltage is a function of the IGBT current. Therefore, the IGBT junction temperature is only related to the IGBT current. The IGBT junction temperature distribution can be changed by changing the IGBT current. By adding a temperature-equalizing fine-tuning virtual impedance to the traditional droop control loop, the current flowing through the IGBTs in each DC / DC converter can be adjusted, so that the IGBT junction temperatures in each parallel DC / DC converter tend to be consistent, thereby improving the overall system reliability. S9. Generate PWM drive signals for parallel DC / DC converters based on voltage and current dual closed-loop control.

2. The method for temperature control of IGBTs in a parallel DC / DC converter of a DC microgrid according to claim 1, characterized in that, The calculation process for IGBT power loss is as follows: IGBT power losses are divided into conduction losses, switching losses, and drive losses. IGBT drive losses account for less than 0.1%, and their impact on IGBT junction temperature calculations can be ignored. IGBT conduction losses are closely related to the IGBT's on-state voltage, the bridge arm current flowing through the IGBT, the IGBT junction temperature, and the duty cycle. In the formula, V ce This is the IGBT turn-on voltage, and its value is related to the IGBT current and the IGBT junction temperature; a (t) represents the current flowing through the IGBT; T j (t) represents the IGBT junction temperature; δ(t) represents the duty cycle; IGBT switching losses are closely related to the current flowing through the IGBT, the DC-side voltage, the IGBT junction temperature, and the IGBT switching frequency. In the formula, E on+off This is the sum of the IGBT turn-on and turn-off losses; f sw U is the IGBT switching frequency; dc K is the DC bus voltage. v U is the DC voltage coefficient; ref This is the DC-side reference voltage.

3. The method for temperature control of IGBTs in a parallel DC / DC converter of a DC microgrid according to claim 1, characterized in that, The IGBT thermal network model is established based on the following: when current flows through the IGBT, the IGBT will generate a certain amount of heat. The heat transfer inside the IGBT is mainly by thermal conduction. The heat transfer is different in different layers of the IGBT, so it is necessary to perform thermal modeling for different layers of the IGBT separately to obtain a one-dimensional equivalent thermal network model inside the IGBT.

4. The method for temperature control of IGBTs in a parallel DC / DC converter of a DC microgrid according to claim 1, characterized in that, The IGBT junction temperature is calculated based on the IGBT power loss and the IGBT thermal network model.

5. The method for temperature control of IGBTs in a parallel DC / DC converter in a DC microgrid according to claim 1, characterized in that, The expression for calculating IGBT junction temperature is: In the formula, T j T represents the junction temperature of the IGBT. a Ambient temperature; , Z represents the electrical losses of the IGBT and the anti-parallel diode. ha This refers to the thermal resistance of the IGBT.

6. The method for temperature control of IGBTs in a parallel DC / DC converter of a DC microgrid according to claim 1, characterized in that, The formula for calculating the average junction temperature of parallel IGBTs is: 。 7. The method for temperature control of IGBTs in a parallel DC / DC converter of a DC microgrid according to claim 1, characterized in that, The difference between the IGBT junction temperature and the average IGBT junction temperature of the parallel DC / DC converter is: 。 8. The method for temperature control of IGBTs in a parallel DC / DC converter of a DC microgrid according to claim 1, characterized in that, The PWM drive signal for the parallel DC / DC converter is generated based on the voltage and current dual closed-loop control.

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