SiC MOSFET junction temperature detection method of photovoltaic grid-connected inverter cabinet

Abstract

The invention discloses a SiC MOSFET junction temperature detection method for a photovoltaic grid-connected inverter cabinet, and the method comprises the steps: building a relation between the threshold voltage and the junction temperature of a SiC MOSFET through an experiment, designing an online junction temperature detection circuit based on a T trigger, avoiding the interference between a gate drive circuit and a main power loop through a Kelvin source packaging technology, achieving the high-precision threshold voltage detection, and achieving the high-precision detection of the junction temperature of the SiC MOSFET. Further, the junction temperature of the SiC MOSFET is obtained; furthermore, in consideration of the influence of the threshold voltage drift of the SiC MOSFET on the junction temperature detection result, the invention provides a drift compensation strategy for updating the junction temperature model and correcting the threshold voltage drift caused by aging when the inverter cabinet is shut down or periodically maintained, thereby improving the long-term stability of the junction temperature detection.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic grid-connected inverter cabinets and power semiconductor device junction temperature detection, and in particular to a non-intrusive SiC MOSFET junction temperature online detection method based on threshold voltage drift compensation, which is suitable for real-time monitoring of the junction temperature of SiC MOSFET in photovoltaic grid-connected inverter cabinets. Background Art

[0002] With the continuous development of photovoltaic power generation technology, the role of photovoltaic grid-connected inverter cabinets in power systems is becoming increasingly important. As a new type of power semiconductor device, SiC MOSFET is gradually replacing traditional silicon-based devices due to its excellent thermoelectric performance and is widely used in photovoltaic grid-connected inverter cabinets. SiC MOSFET has the characteristics of high switching speed, high voltage resistance and high efficiency, which can effectively improve the performance of the inverter in high power density applications. However, during the operation of SiC MOSFET, the increase in junction temperature will have a significant impact on its performance, reliability and life. Real-time monitoring of junction temperature is crucial to improving the reliability of photovoltaic grid-connected inverter cabinets.

[0003] The existing SiC MOSFET junction temperature detection methods can be roughly divided into optical methods, physical contact methods and electrical methods. Although the optical method has the advantages of good resolution and non-contact, it is difficult to perform real-time online monitoring because the device needs to be unsealed or exposed, and it will reduce the reliability of the system. Although the physical contact method can provide higher resolution and low cost, its response time is long, and it is still an invasive measurement method, which cannot meet the needs of online monitoring. The electrical method, especially the junction temperature detection method based on temperature-sensitive electrical parameters (such as the threshold voltage method), does not require additional sensors and can perform real-time online monitoring during the operation of the equipment. It has become an ideal non-invasive junction temperature detection technology. The threshold voltage method can quickly and accurately estimate the junction temperature of the device by measuring the relationship between the threshold voltage Vth and the junction temperature Tj of the SiC MOSFET. However, during the long-term use of SiC MOSFET, the threshold voltage will drift due to the charge capture phenomenon in the gate dielectric, resulting in errors in the junction temperature detection results. Summary of the invention

[0004] In view of the shortcomings in the prior art, the present invention provides a non-intrusive photovoltaic grid-connected inverter cabinet SiC MOSFET junction temperature detection method based on threshold voltage drift compensation, which can monitor the SiC MOSFET junction temperature in real time during the online operation of the photovoltaic grid-connected inverter cabinet, and can further compensate for the threshold voltage drift phenomenon to ensure the accuracy and reliability of junction temperature detection.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A method for detecting junction temperature of SiC MOSFET in photovoltaic grid-connected inverter cabinet:

[0007] During normal operation of SiC MOSFET, the online junction temperature detection circuit monitors the source voltage V in real time. SS' , when the source voltage V SS' Exceeds the set reference voltage V ref When the T trigger triggers the ADC module to start sampling, the gate-source voltage V of the SiCMOSFET is obtained through sampling. GS , which is the threshold voltage V of the current SiC MOSFET th , and then through the threshold voltage V th and junction temperature T j The relationship between the current junction temperature of SiC MOSFET is calculated;

[0008] When the photovoltaic grid-connected inverter cabinet is shut down or undergoing regular maintenance, if the threshold voltage drifts, the threshold voltage drift coefficient k is used to correct the threshold voltage V th and junction temperature T j The relationship between the two is used to obtain the junction temperature of the SiC MOSFET when the photovoltaic grid-connected inverter cabinet is working normally.

[0009] Furthermore, the drift coefficient k of the threshold voltage is:

[0010]

[0011] Among them, V th1 is the threshold voltage obtained without updating the model and without considering the aging effect, V th2 It represents the real value of SiC MOSFET threshold voltage obtained by offline measurement.

[0012] Furthermore, the threshold voltage drift factor k calculated for the same SiC MOSFET junction temperature is added to V th -T j Relationship curve is used to compensate for the drift of threshold voltage. The threshold voltage after compensation is expressed as:

[0013]

[0014] Furthermore, the V th2 The threshold voltage is obtained by using an offline detection circuit, which is composed of a drive circuit and a SiC MOSFET connected in series. The drive circuit includes a power supply, an optocoupler switch, and a current limiting resistor connected in series in sequence, and then connected to the gate resistor and the drain of the SiC MOSFET through a diode D1 and a diode D2 respectively.

[0015] Furthermore, the V th1 After the photovoltaic grid-connected inverter cabinet is shut down, the ambient temperature is used as the junction temperature of the SiC MOSFET, and the relationship between the threshold voltage and the junction temperature is obtained.

[0016] Furthermore, the online junction temperature detection circuit is formed by connecting in series a SiC MOSFET to be tested and a threshold voltage detection circuit based on a T trigger.

[0017] Furthermore, the threshold voltage detection circuit based on the T trigger includes an XOR gate, an AND gate, a NOT gate, a comparator U2, a timer module, an ADC module and a T trigger; during detection, the voltage across the inductor LS between the SiC MOSFET source S and the Kelvin source S' is first collected, and the signal Vcom is obtained after being compared with the reference voltage through the comparator U2. The Vcom is connected to the output nRST of the T trigger through the AND gate to obtain the signal V A , the output nRST of the T flip-flop is the reset signal; the V A Connected to the CLK port of the T flip-flop, where the reset signal pin of the AND gate is output by the V tri The signal is obtained through the timer module and the NOT gate; the V tri The signal and the reference voltage +3V are connected to the T port of the T trigger through an XOR gate. The trigger signal is generated through the Q port of the T trigger to trigger the ADC module. Finally, the ADC module collects the gate-source voltage V of the SiC MOSFET. GS , which is the detection value of the threshold voltage.

[0018] Furthermore, the threshold voltage V th and junction temperature T j The relationship between the current source and the SiC MOSFET to be tested is obtained by building a circuit, measuring the threshold voltage of the SiC MOSFET at different junction temperatures through experiments, and then fitting it.

[0019] The non-intrusive photovoltaic grid-connected inverter cabinet SiC MOSFET junction temperature detection method based on threshold voltage drift compensation proposed in the present invention has the following beneficial effects:

[0020] 1. High-precision junction temperature detection: The present invention achieves high-precision online monitoring of SiC MOSFET junction temperature by establishing an accurate relationship between SiC MOSFET threshold voltage and junction temperature. Experiments show that the junction temperature detection method based on threshold voltage has good linearity and sensitivity (-4.2mV / ℃), and the detection error is less than 3℃, which can accurately reflect the junction temperature change of SiC MOSFET.

[0021] 2. Non-invasive detection: Compared with traditional physical contact and optical methods, the present invention does not require additional installation of sensors, nor does it require unsealing or exposing devices. It uses an online detection method based on the threshold voltage method, and monitors the junction temperature completely through the electrical parameters of the SiCMOSFET itself, avoiding interference and damage to the device. It is suitable for real-time online monitoring of equipment and ensures the reliability and safety of the system.

[0022] 3. Threshold voltage drift compensation: This invention takes into account the drift characteristics of the threshold voltage of SiC MOSFET during long-term use and proposes an effective drift compensation strategy. By updating the junction temperature model when the photovoltaic grid-connected inverter cabinet is shut down or undergoes regular maintenance, the threshold voltage drift caused by SiC MOSFET aging or charge capture can be corrected, thereby ensuring the accuracy and long-term stability of the junction temperature detection results and avoiding the influence of aging on the measurement results.

[0023] 4. Simple and reliable circuit design: The online junction temperature detection circuit designed by the present invention is based on a T trigger and a comparator, and has a simple circuit structure, which is easy to integrate and implement. By using the Kelvin source voltage, the electrical interference between the gate drive circuit and the main power circuit can be effectively avoided, ensuring the high quality and accuracy of the detection signal.

[0024] 5. Strong adaptability: This method is suitable for SiC MOSFET junction temperature detection in photovoltaic grid-connected inverter cabinets, and can also be widely used in other high-power density and high-efficiency power electronic devices. Especially in photovoltaic systems, SiC MOSFET is a key power device, and its junction temperature monitoring is crucial to ensure the safety and stable operation of the system. The present invention provides an efficient and accurate solution.

[0025] 6. High cost-effectiveness: The detection method of the present invention does not require additional external temperature sensors, and uses existing SiCMOSFET electrical parameters for online junction temperature monitoring, thereby reducing the hardware cost and maintenance cost of the system. At the same time, the reliability and monitoring accuracy of the system are improved, with high economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the SiC MOSFET junction temperature detection circuit of the present invention;

[0027] Figure 2 This is a schematic diagram of the threshold voltage test circuit of the present invention;

[0028] Figure 3 This is a diagram of the threshold voltage acquisition and fitting results of the present invention;

[0029] Figure 4 This is a circuit diagram of an online detection circuit of a threshold voltage based on a T trigger according to the present invention;

[0030] Figure 5 The circuit trigger logic diagram of the present invention;

[0031] Figure 6 A flow chart of updating a junction temperature model considering threshold voltage drift compensation according to the present invention;

[0032] Figure 7 This is a schematic diagram of the threshold voltage offline detection circuit of the present invention;

[0033] Figure 8 A schematic diagram of the relationship between the threshold voltage and temperature according to the present invention;

[0034] FIG9( a ) is a physical display diagram of the SiC MOSFET being unsealed before the junction temperature detection according to the present invention;

[0035] FIG9( b ) is a physical representation of the cleaning of the SiC MOSFET before the junction temperature detection according to the present invention;

[0036] FIG9( c ) is a physical display diagram of the SiC MOSFET being smoked before the junction temperature detection according to the present invention;

[0037] Fig.10 This is a comparison chart of junction temperature test results of different methods described in the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0039] The present invention discloses a non-intrusive photovoltaic grid-connected inverter cabinet SiCMOSFET junction temperature detection method based on threshold voltage drift compensation. Figure 1 The main power circuit energy transmission of the photovoltaic grid-connected inverter cabinet is realized by the DC power supply voltage V in After being inverted into a high-frequency AC voltage V by an inverter circuit ab , wherein the inverter circuit adopts an H-bridge type, that is, it contains a total of 4 SiC MOSFETs (S1, S2, S3 and S4); the threshold voltage test circuit includes a conditioning circuit and a threshold voltage detection circuit based on a T trigger, wherein the conditioning circuit includes: a voltage follower, an RC filter (composed of an inductor R S and capacitor C S The threshold voltage detection circuit based on the T trigger includes: an XOR gate, an AND gate, a NOT gate, a comparator U2, a timer module, an ADC module and a T trigger. The specific connection of the threshold voltage detection circuit based on the T trigger is shown in Figure 4 , which will be described in the detection method section.

[0040] The present invention discloses a non-intrusive photovoltaic grid-connected inverter cabinet SiC MOSFET junction temperature detection method based on threshold voltage drift compensation, comprising the following steps:

[0041] S1. Establish a mapping model between the threshold voltage and junction temperature of SiC MOSFET: Figure 2 The circuit schematic diagram shown is Figure 2 The circuit shown in the figure includes a current source and a SiC MOSFET to be tested, where I1 represents the output current of the current source and V DS is the drain-source voltage of SiC MOSFET, V GS represents the gate-source voltage of SiC MOSFET. For the SiC MOSFET to be tested, C GD , C GS and C DS They represent the gate-drain capacitance, gate-source capacitance and drain-source capacitance of SiC MOSFET respectively, R G(int) represents the gate resistance, Q H Represents the SiC MOSFET device body, VD H Represents the parasitic diode. The threshold voltage V of SiCMOSFET at different junction temperatures is measured experimentally. th The specific method is: use a constant temperature heating platform to simulate and set multiple operating temperatures (such as 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ and 100℃, etc.), maintain each temperature condition for 5 minutes to ensure that the temperature is transmitted to the inside of the SiC MOSFET chip, and then collect and record the corresponding threshold voltage.

[0042] The experimental data are fitted, and the fitting results are as follows Figure 3 As shown, the threshold voltage V th and junction temperature T j The relationship between (mapping model), namely equation (1), can convert the change of threshold voltage into the junction temperature of SiC MOSFET.

[0043]

[0044] S2. Design an online junction temperature detection circuit: Design and construct an online junction temperature detection circuit based on SiC MOSFET, which is composed of the SiC MOSFET to be tested and the threshold voltage detection circuit based on T trigger in series. The online junction temperature detection circuit is used to test the voltage between the source and Kelvin source of SiC MOSFET to avoid interference between the gate drive circuit and the main power circuit and ensure the accuracy of the measurement signal. Using components such as T trigger and comparator, the source voltage V is detected when the SiC MOSFET is working. SS'By monitoring the change of this voltage, the threshold voltage V th , and trigger the ADC module to sample. The entire threshold voltage online detection circuit based on the T trigger is as follows Figure 4 As shown, firstly, the voltage across the inductor LS between the SiC MOSFET source S and the Kelvin source S' is collected, and the signal Vcom is obtained after being compared with the reference voltage through the comparator U2. Furthermore, Vcom is connected to the output nRST (reset signal) of the T trigger through the AND gate to obtain the signal V A , V A Connected to the CLK port of the T flip-flop, where the reset signal pin of the AND gate is output by the V tri The signal is obtained through the timer module and the NOT gate. In addition, V tri The signal and the reference voltage +3V are connected to the T port of the T trigger through an XOR gate. The trigger signal is generated through the Q port of the T trigger to trigger the ADC module. Finally, the ADC module collects the gate-source voltage V of the SiC MOSFET. GS , which is the detection value of the actual threshold voltage.

[0045] S3, real-time measurement of the threshold voltage V of SiC MOSFET th :During normal operation of SiC MOSFET, the online junction temperature detection circuit monitors the source voltage V in real time SS' When the source voltage V SS' Exceeds the set reference voltage V ref When the ADC module is triggered by the T trigger to start sampling, the circuit trigger logic diagram is as follows Figure 5 As shown, the gate-source voltage V GS , which is the threshold voltage V of the current SiC MOSFET th , and then through the previously established V th and junction temperature T j The current junction temperature can be calculated using the relationship between

[0046] S4. Update of the junction temperature model (i.e., formula (1)) considering threshold voltage drift compensation: The threshold voltage V of SiC MOSFET th Drift may occur due to long-term use, affecting the junction temperature measurement results. In order to correct this effect, threshold voltage drift compensation is required. When the photovoltaic grid-connected inverter cabinet is shut down or undergoing regular maintenance, read the value T of the ambient temperature sensor. a , at which point the junction temperature of the SiC MOSFET is set to the ambient temperature. Then, the threshold voltage V th2 The threshold voltage in the reference model (i.e., formula (1)) is subtracted (the threshold voltage in the reference model is recorded as V th1), calculate the drift of the threshold voltage, obtain the drift coefficient from the drift, and use the drift coefficient k to correct the V in the junction temperature model. th and junction temperature T j The relationship between and updates the constant term in the junction temperature model. The update process of the entire junction temperature model is as follows: Figure 6 As shown, the specific steps are as follows:

[0047] Step 1: After the photovoltaic grid-connected inverter cabinet is shut down and fully cooled, read the value T of the onboard ambient temperature sensor a , at this time the junction temperature of the SiC MOSFET is equal to the ambient temperature:

[0048] T j =T a (2)

[0049] Step 2: Since the junction temperature of SiC MOSFET is T a , substituting into formula (1), we can get:

[0050] V th1 =3.6281-0.0049T a (3)

[0051] Where V th1 It is the threshold voltage obtained without updating the model and without considering the aging effect.

[0052] Step 3: Turn on the threshold voltage offline detection circuit ( Figure 7 ), since the working states and working time of the four SiC MOSFETs in the photovoltaic grid-connected inverter cabinet are basically the same, for the sake of illustration and to reduce the complexity of the system, only the threshold voltage of one of the SiC MOSFETs is detected. The principle is as follows Figure 7 shown.

[0053] Figure 7 Mainly includes the power supply V in the drive circuit EE =20V, a current limiting resistor R=2kΩ, two diodes D1 and D2 and an optocoupler switch S. When the photovoltaic grid-connected inverter cabinet is working normally, the switch S is disconnected and the current injection is stopped. When the photovoltaic grid-connected inverter cabinet is shut down and threshold voltage detection is required, the switch S is turned on and the driving power supply V EE The input capacitor of the SiC MOSFET is charged, and a 2kΩ current limiting resistor is connected in series to control the current I to about 10mA. Once the gate voltage of the SiC MOSFET reaches the threshold voltage, its drain-source voltage V DS will drop, and the current is conducted through the SiC MOSFET. At this time:

[0054] V th2 =V OUT (4)

[0055] Where V th2 Represents the true value of the SiC MOSFET threshold voltage, V OUT That is, the gate-source voltage collected.

[0056] Step 4: Due to the ambient temperature T a remains constant, the junction temperature of the offline device also remains constant. Comparison threshold voltage V th1 and the threshold voltage true value V th2 The size of V th1 <V th2 , it indicates that the threshold voltage has drifted and drift compensation is required.

[0057] Step 5: The drift compensation amount can be characterized by the drift coefficient k of the threshold voltage:

[0058]

[0059] Step 6: Add the threshold voltage drift coefficient k calculated at the same SiC MOSFET junction temperature to V th -T j The threshold voltage drift is compensated by using the curve (obtained by fitting in S1). The threshold voltage after compensation can be expressed as:

[0060]

[0061] Step 7: After the transformation of formula (6), the junction temperature calculation model of SiC MOSFET is updated as follows:

[0062]

[0063] At this point, the threshold voltage drift compensation of the entire SiC MOSFET junction temperature model is completed for online measurement of junction temperature.

[0064] The updated model can be used again for real-time detection to ensure the accuracy of junction temperature measurement results in long-term use.

[0065] In order to verify the effect of the non-intrusive photovoltaic grid-connected inverter cabinet SiC MOSFET junction temperature detection method based on threshold voltage drift compensation of the present invention, the threshold voltage of SiC MOSFET is tested when it works at different temperatures (30℃, 40℃, 50℃, 60℃, 70℃, 80℃ and 90℃). The results are as follows: Figure 8As shown, it can be seen that the threshold voltage has a good linear relationship with the junction temperature. The junction temperature detection method based on the threshold voltage has good linearity and sensitivity (-4.2mV / ℃) and is not affected by changes in load current. Further, in order to verify the accuracy, the present invention unseals the SiC MOFET, and the infrared temperature probe directly measures the chip temperature as a benchmark to verify the correctness of the junction temperature detection method based on the threshold voltage proposed by the present invention. After the SiC MOSFET is unsealed, as shown in Figure 9(a), it is covered with transparent organic potting gel for insulation; the potting gel is cleaned and removed using Adrox 2312 chemical solvent, as shown in Figure 9(b). Due to the reflective properties of the metal, this state cannot be measured using an infrared temperature probe, so it is smoked black using MOTIP 04031 black high-temperature resistant paint, as shown in Figure 9(c). Fig.10 The temperature information obtained by using the junction temperature detection method and infrared measurement method proposed in the present invention is demonstrated, and the temperature information obtained by using the threshold voltage V th The accuracy of online junction temperature detection is such that the detection error does not exceed 3°C during the operation of the photovoltaic grid-connected inverter cabinet.

[0066] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A method for detecting junction temperature of SiC MOSFET of photovoltaic grid-connected inverter cabinet, characterized in that: During normal operation of SiC MOSFET, the online junction temperature detection circuit monitors the source voltage V in real time. SS' , when the source voltage V SS' Exceeds the set reference voltage V ref When the T trigger triggers the ADC module to start sampling, the gate-source voltage V of the SiC MOSFET is obtained through sampling. GS , which is the threshold voltage V of the current SiC MOSFET th , and then through the threshold voltage V th and junction temperature T j The relationship between the current junction temperature of SiC MOSFET is calculated; When the photovoltaic grid-connected inverter cabinet is shut down or undergoing regular maintenance, if the threshold voltage drifts, the threshold voltage drift coefficient k is used to correct the threshold voltage V th and junction temperature T j The relationship between the two is used to obtain the junction temperature of the SiC MOSFET when the photovoltaic grid-connected inverter cabinet is working normally.

2. The SiC MOSFET junction temperature detection method for a photovoltaic grid-connected inverter cabinet according to claim 1, characterized in that: The drift coefficient k of the threshold voltage is: Among them, V th1 is the threshold voltage obtained without updating the model and without considering the aging effect, V th2 It represents the real value of SiC MOSFET threshold voltage obtained by offline measurement.

3. The SiC MOSFET junction temperature detection method for a photovoltaic grid-connected inverter cabinet according to claim 2, characterized in that: Add the threshold voltage drift factor k calculated for the same SiC MOSFET junction temperature to V th -T j Relationship curve is used to compensate for the drift of threshold voltage. The threshold voltage after compensation is expressed as:

4. The SiC MOSFET junction temperature detection method for a photovoltaic grid-connected inverter cabinet according to claim 2, characterized in that: The V th2 The threshold voltage is obtained by using an offline detection circuit, which is composed of a drive circuit and a SiC MOSFET connected in series. The drive circuit includes a power supply, an optocoupler switch, and a current limiting resistor connected in series in sequence, and then connected to the gate resistor and the drain of the SiC MOSFET through a diode D1 and a diode D2 respectively.

5. The SiC MOSFET junction temperature detection method for a photovoltaic grid-connected inverter cabinet according to claim 2, characterized in that: The V th1 After the photovoltaic grid-connected inverter cabinet is shut down, the ambient temperature is used as the junction temperature of the SiC MOSFET, and the relationship between the threshold voltage and the junction temperature is obtained.

6. The SiC MOSFET junction temperature detection method for a photovoltaic grid-connected inverter cabinet according to claim 1, characterized in that: The online junction temperature detection circuit is formed by connecting a SiC MOSFET to be tested and a threshold voltage detection circuit based on a T trigger in series.

7. The SiC MOSFET junction temperature detection method for a photovoltaic grid-connected inverter cabinet according to claim 6, characterized in that: The threshold voltage detection circuit based on the T trigger includes an XOR gate, an AND gate, a NOT gate, a comparator U2, a timer module, an ADC module and a T trigger. During detection, the voltage across the inductor LS between the SiC MOSFET source S and the Kelvin source S' is first collected, and the signal Vcom is obtained after being compared with the reference voltage through the comparator U2. The Vcom is connected to the output nRST of the T trigger through the AND gate to obtain the signal V A , the output nRST of the T flip-flop is the reset signal; the V A Connected to the CLK port of the T flip-flop, where the reset signal pin of the AND gate is output by the V tri The signal is obtained through the timer module and the NOT gate; the V tri The signal and the reference voltage +3V are connected to the T port of the T trigger through an XOR gate. The trigger signal is generated through the Q port of the T trigger to trigger the ADC module. Finally, the ADC module collects the gate-source voltage V of the SiC MOSFET. GS , which is the detection value of the threshold voltage.

8. The SiC MOSFET junction temperature detection method for a photovoltaic grid-connected inverter cabinet according to claim 1, characterized in that: The threshold voltage V th and junction temperature T j The relationship between the current source and the SiC MOSFET to be tested is obtained by building a circuit, measuring the threshold voltage of the SiC MOSFET at different junction temperatures through experiments, and then fitting it.

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