Fault-Tolerant Power Amplification
Darian Retianza defended his PhD thesis at the department of Electrical Engineering on January 31st.
For his PhD research Darian Retianza successfully created a method to improve the fault-tolerant capability of the power amplifier in two stressing problems: short-circuiting in a GaN Half Bridge and the current sensor error. By implementing the proposed stray-inductance-based short-circuit detection, ultra-fast protection in a Half Bridge (less than 100 ns) can be realized. In addition, by implementing the proposed sensor error compensation methods, it is successfully proved that current sensor errors are possibly reduced to 1% of the initial error, improving position accuracy mainly in the high-precision mechatronics applications.
The failure mechanisms of two different mechatronics systems, i.e., an Electromagnetic Active Suspension System and a High Precision Wafer Positioning System, are studied based on literature studies. The failure analysis is used to find options for improving the fault-tolerant capability of power electronics systems in these applications. For one system, a binary fault in the form of a short circuit in a half-bridge is addressed. Later, drift faults typically appearing in sensors are investigated, and methods to counteract their influence are developed. These methods, which allow the elimination of additive errors such as drift and gain faults, are applied to current sensors in a motion system driven by a three-phase actuator.
The first research objective is to create objective metrics to justify fault-tolerant topologies and redundancy of power amplifiers. A power amplifier topology's fault-tolerant and redundant structure is analyzed by considering system reliability, power, density, and efficiency. The analysis evaluates the topological possibility of employing a multiphase system, a multilevel converter, and wide-band gap (WBG) devices.
Ultra-fast short circuit protection
The second research objective is to achieve ultra-fast short circuit protection in power amplifiers in many mechatronic applications. Two inductance-based short circuit protection methods are developed for ultra-fast short circuit detection. These short circuit protection methods are denoted as Stray Voltage Capture (SVC) and Extended Stray Voltage Capture (ESVC). Non-linear simulation models and analytical modelling methods are presented. These provide the design criteria needed for the component parameter choice of SVC and ESVC. The work is completed by experimental verification, where the results indicate some limitations for which possible solution directions are given. The possibility of applying the methods in low-impedance circuits, such as a loop in GaN and SiC devices, is also evaluated. Additional design criteria, such as the proper choice of decoupling capacitors, are described. As a spin-off of the SVC and ESVC methods, another method called Stray Field Capture (SFC) is proposed. SFC is also tested in an experimental setup; a three-phase converter-based GaN device is used for the evaluation.
Identifying and compensating errors
The third research objective, identifying and compensating for errors in a three-phase current sensing system, is achieved using mathematical relations between the measured current and the estimated current. The three-phase system's current errors (gain and offset) are identified and compensated with or without the machine plant. These methods do not incorporate additional hardware, making them low-cost and straightforward in their implementation. System modelling and analytical derivation are presented. The solution is applied in a highly dynamic application, i.e., a high-precision wafer stage positioning system and an application in standstill condition. The analytical, simulation and laboratory experiments demonstrate the validity of the proposed method.
Title of PhD thesis: Fault-Tolerant Power Amplification. Supervisors: Henk Huisman and Bas Vermulst.