Inverter Gate Drive for Shorter Dead Time in SiC MOSFETs
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Solution Overview
Problem
Inverter devices experience significant losses and conduction deterioration due to the large forward voltage drops of parasitic diodes during dead time, especially when using SiC MOSFETs, leading to increased energy loss and potential damage from through currents.
Innovation Solution
The implementation of a decision circuit, gate driver, and voltage step-down/shutoff circuit configuration that allows the MOSFETs to handle reflux currents instead of parasitic diodes during dead time, reducing the dead time and minimizing voltage drops across MOSFETs, thereby reducing energy losses and preventing conduction deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead time is provided to avoid short-circuit between upper and lower arms, then through current is prevented, but loss increases due to large forward voltage drops of parasitic diodes
Solution Approach 1:
A capacitor is introduced as an intermediary energy storage element between the DC power supply and the inverter bridge. This capacitor supplies energy during dead time to maintain voltage levels, allowing the use of shorter dead time periods while preventing the energy loss that would otherwise occur through parasitic diodes.
Solution Approach 2:
The capacitor is pre-charged to a specific voltage level before dead time occurs. This preliminary energy storage enables the system to bridge the dead time period without relying on parasitic diodes, thereby reducing energy loss while maintaining reliable operation.
2Loss of energy
If SiC MOSFETs are used to reduce forward voltage drop, then efficiency is improved, but conduction deterioration occurs more readily in parasitic diodes
Solution Approach 1:
The capacitor serves as a protective intermediary that eliminates the need for prolonged parasitic diode conduction. By providing energy during dead time, it prevents the conduction deterioration that would otherwise occur in SiC MOSFET parasitic diodes, allowing the system to fully utilize the low loss characteristics of SiC devices.
Solution Approach 2:
The invention converts the potential harm of dead time (which causes parasitic diode conduction and deterioration) into a benefit by using the capacitor to actively manage the dead time period. This allows the system to achieve both the efficiency benefits of SiC MOSFETs and the reliability of stable parasitic diode characteristics.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly shortens dead time, reduces energy losses, and maintains good conduction characteristics for SiC MOSFETs, even during regenerative running, by ensuring reflux currents flow through the MOSFETs rather than parasitic diodes, thus enhancing efficiency and longevity.
Implementation Method 1
a phenomenon called conduction deterioration may be generated in which characteristics of the parasitic diode deteriorate
Data Source
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AI summary
To provide an inverter device and an electric motor device using the same to shorten a dead time. Thus, an inverter device (140) is provided, which includes: a switching element (101h) including a control terminal and a pair of main terminals; a control circuit (110) configured to output a control signal (V1h) which indicates whether to instruct an ON state of the switching element (101h); a decision circuit (103) configured to output a decision signal (V2h) which indicates a state of the switching element (101h) based on a voltage (Vdh-Vsh) between the main terminals of the switching element (101h); and a drive circuit (104, 105) configured to control the ON state or an OFF state of the switching element (101h) based on the control signal (V1h) and the decision signal (V2h).