In this paper, a novel control strategy is presented for reinforcement learning with disturbance compensation to solve the problem of quadrotor positioning under external disturbance. The proposed control scheme applies a trained neural-network-based reinforcement learning agent to control the quadrotor, and its output is directly mapped to four actuators in an end-to-end manner. The proposed control scheme constructs a disturbance observer to estimate the external forces exerted on the three axes of the quadrotor, such as wind gusts in an outdoor environment. By introducing an interference compensator into the neural network control agent, the tracking accuracy and robustness were significantly increased in indoor and outdoor experiments. The experimental results indicate that the proposed control strategy is highly robust to external disturbances. In the experiments, compensation improved control accuracy and reduced positioning error by 75%. To the best of our knowledge, this study is the first to achieve quadrotor positioning control through low-level reinforcement learning by using a global positioning system in an outdoor environment.

We present a detailed study of dynamic switching instability and static reliability of a Gallium Nitride (GaN) Metal-Insulator-Semiconductor High-Electron-Mobility-Transistor (MIS-HEMT) based cascode switch under off-state (negative bias) Gate bias stress (V_{GS, OFF}). We have investigated drain channel current (I_{DS, Max}) collapse/degradation and turn-on and rise-time (t_R) delay, on-state resistance (R_DS-ON) and maximum transconductance (G_{m, max}) degradation and threshold voltage (V_TH) shift for pulsed and prolonged off-state gate bias stress V_{GS, OFF}. We have found that as stress voltage magnitude and stress duration increases, similarly I_{DS, Max} and R_DS-ON degradation, V_TH shift and turn-on/rise time (t_R) delay, and G_{m, max} degradation increases. In a pulsed off-state V_{GS, OFF} stress experiment, the device instabilities and degradation with electron trapping effects are studied through two regimes of stress voltages. Under low stress, V_TH shift, I_DS collapse, R_DS-ON degradation has very minimal changes, which is a result of a recoverable surface state trapping effect. For high-stress voltages, there is an increased and permanent V_TH shift and high I_{DS, Max} and R_DS-ON degradation in pulsed V_{GS, Stress} and increased rise-time and turn-on delay. In addition to this, a positive V_TH shift and G_{m, max} degradation were observed in prolonged stress experiments for selected high-stress voltages, which is consistent with interface state generation. These findings provide a path to understand the failure mechanisms under room temperature and also to accelerate the developments of emerging GaN cascode technologies.

This paper reports an extensive analysis of the physical mechanisms responsible for the failure of GaN-based metal–insulator–semiconductor (MIS) high electron mobility transistors (HEMTs). When stressed under high applied electric fields, the traps at the dielectric/III-N barrier interface and inside the III-N barrier cause an increase in dynamic on-resistance and a shift of threshold voltage, which might affect the long term stability of these devices. More detailed investigations are needed to identify epitaxy- or process-related degradation mechanisms and to understand their impact on electrical properties. The present paper proposes a suitable methodology to characterize the degradation and failure mechanisms of GaN MIS-HEMTs subjected to stress under various off-state conditions. There are three major stress conditions that include: V_DS = 0 V, off, and off (cascode-connection) states. Changes of direct current (DC) figures of merit in voltage step-stress experiments are measured, statistics are studied, and correlations are investigated. Hot electron stress produces permanent change which can be attributed to charge trapping phenomena and the generation of deep levels or interface states. The simultaneous generation of interface (and/or bulk) and buffer traps can account for the observed degradation modes and mechanisms. These findings provide several critical characteristics to evaluate the electrical reliability of GaN MIS-HEMTs which are borne out by step-stress experiments.