The sensorless control algorithm operates over a continuous speed range of 10 to 100% of full speed without overload for greater performance. Removing the Hall sensors reduces the motor’s cost while significantly improving reliability.
The module is designed to shut down during an overcurrent, overtemperature, or an over- and undervoltage event. Phase currents are monitored. If the safe condition is exceeded, a gate kill signal is applied and a fault occurrence is indicated. At this point, a restart sequence can be initiated which includes clearing the fault.
A thermistor is mounted on the IMS substrate board close to the power silicon. If the substrate temperature exceeds the safe limit of 105 degrees C, a gate-kill signal is asserted. The DC bus is also monitored for under-voltage and over-voltage conditions and minimum and maximum speed conditions. Operation outside these preset limits will also produce a fault to protect the load. To clear the fault condition, a fault clear pin is provided to initiate restart. Communication to the device is done via an RS-232 serial interface and can be used for longer cable lengths or noisy environments. Additionally, the module uses an error detecting protocol to maintain the integrity of the host registers.
Optimized Power Stage
Based on selected parameters, the proprietary algorithm within the digital controller ultimately controls the gate driver in the motor control module and the switching of the power semiconductors during commutation.
The optimized chipset—including the control, gate drive and power MOSFETs and intellectual property—is combined with rugged packaging to meet vibration profiles in a small lightweight package ready to mount on a cold plate or heatsink.
This integrated package incorporates a fully qualified power MOSFET mounted on an insulated metal substrate (IMS) close to the gate drivers for the lowest possible inductance. Each lot is screened to military specification MIL-PRF-38534 to ensure the highest level of reliability and rated at the full operating temperature range of -40 to +85 degrees Celsius.
Since the control algorithm is a hardware-based IC dedicated to motor control, certification requirements are simpler than those designed for a software-based algorithm programmed into a microcontroller or FPGA, resulting in a rapid, cost effective time-to- market solution for electric aircraft system integrators.
A companion development tool expedites software development by providing a simple menu-based selection process where motor design and user defined parameters such as ramp time or maximum speed are organized a drive parameter spreadsheet. Upon completing motor design, the final design parameters and the user defined parameters are entered into the development spreadsheet. The development tool then translates the motor parameters and stores them within the module, enabling the motor designer to quickly evaluate the motor’s performance. Diagnostic tools are also available to aid this process.
This article was contributed by Michael Toland, Product Marketing Manager, International Rectifier, El Segundo, CA. For more information, visit http://info.hotims.com/15124-322.