“ST’s six-phase motor fault-tolerant control solution is reliable and stable enough to maintain motor speed stably even when two or three or more phases are faulty, with fault detection and compensation functions.”

STMicroelectronics held the 'ST 6-Phase Drive System Webinar' through e4ds eeWebinar on the 29th.

“If a fault occurs in the motor system, it may not be able to generate the torque required by the application, which could lead to a dangerous situation,” said ST’s Hyunwoo Choi, who was in charge of the presentation that day. “To solve this problem, fault-tolerant technology is needed.”

Motor failure can occur due to various causes. Typical causes include: △ failure of the motor itself, such as open–phase, short-circuit, or missing connection; △ sensor failure, such as malfunction of the winch sensor or current sensor; △ inverter problems, such as power transistor phase failure or gate driver failure.

These problems prevent the system from functioning properly. Especially in a three-phase motor, if one phase fails, the direction of current flow cannot be controlled, making normal rotation impossible.

To address these issues, ST has proposed a fault-tolerant control solution utilizing a six-phase motor system.

A six-phase motor reduces the current flowing in each phase to half that of a three-phase motor when generating the same torque. This lower current increases system efficiency and reduces heat generation, improving efficiency. The phases are spaced 60 degrees apart, resulting in less current ripple than a three-phase inverter. Additionally, as long as three or more of the six phases are operating normally, the motor can continue to operate, allowing the system to continue operating.

With these advantages, ST has developed a 6-phase motor inverter with fault detection and response functions to ensure high reliability.

This inverter is designed to ensure continuous operation even when up to three phases fail simultaneously, using fuses and relays to quickly isolate a failed phase and allow the remaining healthy phases to compensate for the magnetic flux and continue operation.

Additionally, it is evaluated as a powerful solution that can be used in industrial and automotive systems as it includes FOC (Field-Oriented Control) support, current and voltage sensing, and short/open detection functions.

Looking at the main specifications, the power input is 250-400V DC link voltage, the output is a maximum of 1.5㎾, the current capacity is 14A (RMS), and the peak is 20A.

The MCU is a 170㎒ Cortex-M4 core based on STM32G4, and is modular in design for easy maintenance, and can utilize encoders, Hall sensors, resolvers, etc.

Looking at how the system detects and responds to faults, when a fault occurs, the failed phase is rapidly isolated from the DC link within microseconds, and the motor terminals are isolated from the failed leg within milliseconds.

It analyzes the output voltage and PWM command signal to detect short and open conditions, and applies a current compensation algorithm to maintain normal torque after a fault occurs, allowing the remaining normal phases to compensate for the magnetic flux and continue operating.

ST has tested the failure detection and compensation functions in a 700 RPM environment with two and three or more phases failing.It has been confirmed that this is working normally and quickly recovers to the set speed.

It is explained that the compensation algorithm is applied within milliseconds after a failure occurs to maintain normal operation, and that it can guarantee high reliability, especially in automotive, aviation, and industrial applications.

“The 6-phase motor fault tolerance solution is an optimized technology for continuously operating the system even after a fault occurs,” said Manager Choi Hyun-woo, concluding the webinar.