HVDC technology enables efficient transmission of large power amounts over long distances using direct current. There are two main HVDC technologies namely, line-commutated converters (LCC) with thyristors and self-commutated voltage source converters (VSC) with insulated gate bipolar transistors (IGBTs):
- LCC-based HVDC systems consume reactive power and require AC filters for compensation. Power reversal involves voltage polarity reversal, which can be problematic for HVDC grids.
- VSC-HVDC systems produce high-frequency harmonics but require smaller AC filters. For power reversal, voltage polarity remains unchanged, but they have higher losses than LCC technology.
Reverse Asymmetric Bypass Thyristors play a crucial role in high voltage direct current (HVDC) applications, particularly in Voltage Source Converters (VSCs) conducting the DC fault current.
Dynex Reverse Asymmetric Bypass Thyristor
Modern modular multilevel VSC HVDC systems designed around the latest 6.5kV trench IGBT modules use a topology where an equivalently voltage rated bypass thyristor is connected across the antiparallel diode (FRD) of the IGBT to provide resettable protection from ground DC faults with a current exceeding multiple times the FRD rating.
The 6.5kV reverse asymmetric bypass thyristor is a novel device designed bespoke for the application. The reverse configuration utilizes a buffer on the cathode side allowing for the use of thinner silicon which reduces the voltage drop (Vt) while maintaining the 6.5kV reverse blocking rating with a low leakage current. Coupled with an optimized gate pattern the novel design reduces the required anode-side triggering voltage, significantly enhancing the protection of the fast recovery diode (FRD).
Added benefits of these design features are reduced on-state voltage, significantly reduced FIT rating and improved surge current ratings compared to equivalently sized devices allowing for a reduced overall system footprint and matching the increased current requirement for the state of the art trench IGBTs.
Key Features
- Lower forward voltage drop (VT)
- Increased surge current capability
- Reduced required on anode-side voltage for triggering the thyristor (Low pick up voltage)
- Maintain low leakage currents
- Reduced FIT rating
In summary, reverse asymmetric bypass thyristors contribute significantly to HVDC system reliability by swiftly handling faults and ensuring continuous power transmission.
Should you require any specific adjustments to meet unique requirements, please contact us. We are equipped to develop customised products tailored to your needs.