The Research On The Key Technology Of High-voltage Solid Switch

High voltage direct current(HVDC)transmission system is an important solution for massive integration of renewable energy,however,HVDC breaker has been a bottleneck for the development of DC power grid.Traditional mechanical circuit breakers can not meet the requirements of quickness and controllability in HVDC system.Its breaking time is relatively long,and the arc is likely to occur when the load is disconnected,leading to short life.This paper describes the solid-state HVDC breaker based on semiconductors connected in series or parallel and the hybrid HVDC breaker.The key component of the solid-state HVDC breaker – the high voltage solid-state switch is deeply studied.Technical difficulties in the high voltage solid-state switch are how to achieve synchronous drive and isolation between power and control circuits,how to achieve voltage and current equalization when devices connected in series or parallel,and how to reduce its drive power and on-state loss.This paper chooses SiC MOSFET as the main power device,and has analyzed its working characteristics and the effects of parasiticsin.The current imbalance of devices in parallel and the improvement measures have been analyzed in detail.The isolation drive of SiC MOSFET is realized by magnetic coupling,ensuring isolated synchronous drive.This paper has studied a high frequency carrier isolation drive method.In addition,this paper has designed corresponding Gate Isolation Buffer Circuit,Pulse Signal Generation Circuit,Signal Regulating Circuit and H-bridge power drive circuit,achieving the transmission of low-frequency PWM signal and DC transmission of the control signal in transformer isolation mode.This paper has analyzed the causes of the voltage imbalance of SiC MOSFETs in series,and designed an improved Dynamic Active Gate Clamped network for voltage equalization.This paper has designed a high-voltage solid-state switch consisting of nine SiC MOSFETs.By Saber simulation analysis and experimental verification,the duty of control signal is adjustable in 0~100% when the frequency is low.The voltage balance performance achieves satisfying resu lts.In the condition of 1Hz control frequency,the drive power consumption is only 0.1W,proving the practicability and feasibility of the scheme.