High-Temperature Brushless DC Motor Controller Design

Abstract

High-temperature geothermal exploration requires a wide array of tools and sensors to instrument drilling and monitor downhole conditions. There is a steep decline in component availability as the operating temperature increases, limiting tool availability and capability for both drilling and monitoring. Several applications exist where a small motor can provide a significant benefit to the overall operation. Applications such as clamping systems for seismic monitoring, televiewers, valve actuators, and directional drilling systems would be able to utilize a robust motor controller capable of operating in these harsh environments. The development of a high-temperature motor controller capable of operation at 225°C significantly increases the operating envelope for next generation high temperature tools and provides a useful component for designers to integrate into future downhole systems. High-temperature motor control has not been an area of development until recently as motors capable of operating in extreme temperature regimes are becoming commercially available. Currently the most common method of deploying a motor controller is to use a Dewared, or heat shielded tool with low-temperature electronics to control the motor. This approach limits the amount of time that controller tool can stay in the high-temperature environments and does not allow for long-term deployments. A Dewared approach is suitable for logging tools which spend limited time in the well however, a longer-term deployment like a seismic tool [Henfling 2010], which may be deployed for weeks or even months at a time, is not possible. Utilizing high-temperature electronics and a high-temperature motor that does not need to be shielded provides a reliable and robust method for long-term deployments and long-life operations.