K. Sampayan, S. Sampayan
Keywords: Optical Transconductance Varistor, power electronics, photoconductive switching, high voltage, grid technology, energy conversion
Summary:Power electronic systems use specialized semiconductor devices with high voltage and current handling capability to convert electrical energy from one form to another such as AC to DC or one voltage to another. They are used widely in renewable energy inverters, electrical grid protection devices, electric vehicles, data center power systems, medical equipment and much more. It is estimated that by 2030, 80% of all electricity will be processed through power electronics. However, semiconductors now on the market are limited in the voltage a single device can handle. For higher voltages, many devices must be used, introducing difficulties in timing of operation. Also, the drift region inherent in these devices imposes a trade-off between sufficient thickness to hold voltage and rapid charge carrier transit time for on-off transition. Slow transition times and limited switching rates waste energy through transition loss in the devices and hysteresis loss in external magnetic components. Light controlled, bulk conduction devices, where carriers are generated and controlled nearly simultaneously throughout the device volume, provide much higher speed and minimize losses while providing sufficient material thickness to hold off high voltage. Such devices are possible using below bandgap excitation of semi-insulating (SI) silicon carbide (SiC) single crystals. Under a grant from the Advanced Research projects Agency-Energy (ARPA-E, Opcondys, Inc. has demonstrated the Optical Transconductance Varistor (OTV), a new class of efficient, high-speed, high-gain, bi-directional, optically-controlled transistor-like power device. Prototypes operate at multi-10s of kW and 20 kV, exploiting bulk conduction via direct photon-carrier excitation with below bandgap light. Frequency operation of >125 kHz is more than six times that of existing semiconductor devices. Transition times of less than 10 nanoseconds in multi-kilovolt devices allow very fast switching while the linear response of conductivity to optical power provides great control. When used in power electronic systems, the OTV will enable equipment that improves grid reliability, resiliency and efficiency by empowering advanced equipment such as devices that will quickly react to protect the grid in cases of lightning strikes, electromagnetic pulse, geomagnetic disturbances, and other abnormal transients. The device also greatly reduces the size and cost of pulsed power systems used for fusion energy, medical treatment equipment, industrial process and research apparatus. Opcondys is continuing development of a compact OTV module that incorporates the SiC switch material, light source, electrical connectors and heat mitigation in a single package. This single device will replace dozens or hundreds of existing semiconductor devices in high power applications, increasing system reliability and reducing costs for end users.