Adaptive, low-capacitance power supply for gate driving in low-voltage converters
Wallendahl, Anton (2024)
2024
Sähkötekniikan DI-ohjelma - Master's Programme in Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2024-05-02
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202404254606
https://urn.fi/URN:NBN:fi:tuni-202404254606
Tiivistelmä
Silicon carbide metal-oxide-semiconductor field-effect transistors (SiC-MOSFETs) have become available for the semiconductor market. The new type is more suitable for <= 1 kV converter applications than previous MOSFETs. Using SiC-MOSFETs, it is possible to increase the efficiency of the converter and reduce its physical size by increasing the switching frequency. This thesis explores how to produce a bipolar gate voltages in the electric vehicle (EV) direct current (DC) charging system. The objective is to design and manufacture an adjustable and low-capacitance power supply with 3 floating, bipolar outputs. The output voltage ranges are 15V – 20 V and 0V – −5 V, with the required power of 1W per output, i.e. total of 6 W.
The theoretical part discusses the structure of the EV DC charger, the characteristics of SiC-MOSFETs and the operating principles of gate drivers. The insulation requirements for EV charging systems and their impact on gate driving will be reviewed. The work explores the parasitic properties of the transformer and the disturbances conducted through them. Based on simulations, a SiC-MOSFET half-bridge bridge may generate >= 0.20 V interference voltage to the control signals. After comparing gate driving techniques, a commercial gate driver powered by a push-pull converter was found to be the best option. The proposed power supply is the cascade of a buck converter and a constant duty cycle push-pull converter. In this way, the transformer core does not saturate when adjusting the gate voltages. A prototype of the push-pull converter is manufactured and tested with designed custom transformers.
Measurements prove that with the proposed power supply, gate voltages can be adjusted and costs can be cut by up to 62 %. The interwinding capacitance 7.60 pF of the transformer is lower than in commercial implementations when it is related to the number of parallel outputs. The output voltages of the push-pull converter were between 15.15 V – 15.97 V / −2.43 V – −2.49 V and 25.55 V – 26.17 V / −4.42 V – −4.49 V, when measured at 15 V and 22 V input voltages. The efficiency of the prototype was approximately 70 %. A change to a full-wave rectifier, and fine-tuning the turns ratio would make the output voltages closer to the ideal and increase efficiency. The designed buck converter should be manufactured and tested for the voltage regulation of the cascaded system. In measurements, the output voltages of the unregulated push-pull converter rose over 4 V, when the load was disconnected.
The theoretical part discusses the structure of the EV DC charger, the characteristics of SiC-MOSFETs and the operating principles of gate drivers. The insulation requirements for EV charging systems and their impact on gate driving will be reviewed. The work explores the parasitic properties of the transformer and the disturbances conducted through them. Based on simulations, a SiC-MOSFET half-bridge bridge may generate >= 0.20 V interference voltage to the control signals. After comparing gate driving techniques, a commercial gate driver powered by a push-pull converter was found to be the best option. The proposed power supply is the cascade of a buck converter and a constant duty cycle push-pull converter. In this way, the transformer core does not saturate when adjusting the gate voltages. A prototype of the push-pull converter is manufactured and tested with designed custom transformers.
Measurements prove that with the proposed power supply, gate voltages can be adjusted and costs can be cut by up to 62 %. The interwinding capacitance 7.60 pF of the transformer is lower than in commercial implementations when it is related to the number of parallel outputs. The output voltages of the push-pull converter were between 15.15 V – 15.97 V / −2.43 V – −2.49 V and 25.55 V – 26.17 V / −4.42 V – −4.49 V, when measured at 15 V and 22 V input voltages. The efficiency of the prototype was approximately 70 %. A change to a full-wave rectifier, and fine-tuning the turns ratio would make the output voltages closer to the ideal and increase efficiency. The designed buck converter should be manufactured and tested for the voltage regulation of the cascaded system. In measurements, the output voltages of the unregulated push-pull converter rose over 4 V, when the load was disconnected.