Brushless Motor Inverter Switch Protection via Zero-Current Timing
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Solution Overview
Problem
Power semiconductor switches in brushless electric motors are prone to damage when switching off inductive loads, particularly in safety-critical applications like electromechanical steering, due to the release of significant inductive energy, which can exceed their absorption capacity.
Innovation Solution
The method involves a microcontroller that detects defective switches and switches off the AC converter by opening power semiconductor switches at predefined motor position angles where the drain current is zero or negative, preventing damage and allowing safe disconnection of inductive loads without the need for direct current monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If power semiconductor switches are used to control brushless motors, then the switching speed and control precision are improved, but the switches are prone to damage from inductive energy when switching off loads
Solution Approach 1:
The microcontroller determines motor position angles in advance and uses this information to control the timing of power semiconductor switch operations. By pre-calculating the appropriate switching moments based on motor position, the system ensures that switches are opened only when drain current is zero or negative, preventing damage from inductive energy while maintaining high switching speed
Solution Approach 2:
The patent replaces mechanical relays with power semiconductor switches controlled by a microcontroller. Instead of using mechanical contactors that can handle high inductive energy, the system uses electronically controlled MOSFETs or IGBTs with precise timing control based on motor position angles, achieving both high switching speed and protection against inductive damage
2Reliability
If mechanical relays are used instead of power semiconductor switches, then the absorption capability of inductive energy is improved, but the device complexity and size increase
Solution Approach 1:
The patent replaces mechanical relays with solid-state power semiconductor switches (MOSFETs or IGBTs) controlled by a microcontroller. The microcontroller uses motor position angle information to determine the optimal timing for opening switches, ensuring that inductive energy does not damage the semiconductor devices. This electronic control system achieves the same protective function as mechanical relays but with greater compactness, lower complexity, and higher reliability
Solution Approach 2:
The system changes the operating parameters of power semiconductor switches by controlling them based on motor position angles rather than using fixed timing or mechanical actuation. By adjusting the switching timing parameter according to real-time motor position feedback, the system optimizes both the protective function and the efficiency of the switching devices
3Reliability
If suppressor diodes are added to divert inductive energy, then the protection of power semiconductor switches is improved, but the device complexity and cost increase
Solution Approach 1:
The patent replaces passive protective components like suppressor diodes with an active control system based on a microcontroller that uses motor position angle information. Instead of adding hardware components to divert energy, the system uses intelligent timing control to prevent harmful current flow through the switches in the first place, reducing circuit complexity while maintaining protection
Solution Approach 2:
The microcontroller uses the motor position angle information that is already being generated for motor control purposes and repurposes it to determine optimal switching timing for protection. This self-service approach uses existing system resources (position angle data) to provide additional protective function without requiring separate sensing or control hardware
Data Source
AI summary
The invention relates to a method for operating a brushless electric motor, the windings of which are controlled by an inverter using six switches, wherein the inverter comprises three outputs, which are associated with the windings of the electric motor, and wherein a respective power semiconductor switch is arranged between the output of the inverter and the windings, and wherein a detection unit for detecting defective switches, a unit for measuring the voltage at the outputs of the inverter, and a microcontroller for controlling switches are provided. The invention further relates to a device operating a brushless electric motor. In order not to damage the power semiconductor switches, according to the invention of the inverter is switched off by the microcontroller after a defective switch has been detected, such that no additional power is introduced in the windings (U, V, W) of the electric motor and the power semiconductor switches are opened in a predetermined motor angle position (φU, φv, φw). For said purpose, the motor angle positions (φu, φv, φw) are associated with a respective winding (U, V, W) and the power semiconductor switches thereof and are selected such that the associated power semiconductor switches are not damaged during opening.