Brushless Motor Switch Defect Detection via Voltage Measurement
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Solution Overview
Problem
Existing methods for identifying defective switches in brushless electric motors with six switches are costly and require current sensors, limiting the ability to quickly determine the type of defect and operate the motor in an emergency mode.
Innovation Solution
The method involves identifying a defective switch by applying different pulse-width-modulated voltages to windings not associated with the defective switch, measuring the voltage on the affected winding, and determining the defect type based on the duty ratio, without using current sensors, allowing for emergency operation by opening or disabling the defective switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current sensors are used to identify defective switches, then the defect type can be determined, but the costs increase
Solution Approach 1:
The patent uses voltage measurements as an intermediary method to indirectly identify defective switches. Instead of directly measuring current with expensive sensors, the system measures voltages at inverter outputs and uses these voltage readings to infer the state of switches and detect defects, thereby achieving reliable defect identification without current sensors
Solution Approach 2:
The patent replaces the electrical measurement system (current sensors) with a voltage measurement and evaluation system. By substituting current measurement with voltage measurement and logical evaluation of switching states, the system achieves the same defect detection functionality at lower cost
2Reliability
If the electric motor is switched off when a switch defect occurs, then safety is ensured, but emergency mode operation is not possible
Solution Approach 1:
The patent segments the six switches into functional groups and identifies which specific switch is defective. By locating the exact defective switch, the system can isolate only the affected phase or winding while keeping other phases operational, enabling continued emergency mode operation while maintaining safety
Solution Approach 2:
The patent changes the operational parameters of the motor system by switching from normal three-phase operation to emergency mode operation with reduced phases. The control system adapts by modifying voltage application patterns and switching sequences to accommodate the defective switch while maintaining safe and functional operation
3Ease of manufacture
If voltage measurement is carried out on the winding associated with the defective switch, then the defect type can be determined without current sensors, but the method complexity increases
Solution Approach 1:
The patent applies periodic voltage pulses with specific duty cycles (33% and 66%) to the windings and periodically measures the resulting voltages. This periodic excitation and measurement approach creates a systematic evaluation method that, while requiring multiple measurement steps, follows a regular pattern that simplifies the control logic and makes the complex process manageable
Solution Approach 2:
The patent performs preliminary actions by first identifying a defective switch through initial voltage measurements before proceeding to the detailed defect type determination. This preliminary identification step organizes the measurement process and reduces the complexity of subsequent defect characterization by narrowing down the search space
Data Source
AI summary
The present invention relates to a method for operating a brushless electric motor whose windings are driven by an inverter with the aid of six switches, having an identification unit being provided in order to identify defective switches, a unit for voltage measurement at the outputs of the inverter, and a microcontroller for controlling the switches. Particularly in safety-relevant applications, it is important to quickly determine what characteristic the defective switch has, for example in order to continue to operate the electric motor in an emergency mode, or to switch it off immediately. The defect (F1, F2, F3) is traced and the nature of the defect (F1, F2, F3) in a switch determined by using a different voltage (PWM1, PWM2) to drive those windings (V, W) which are not associated with the defective switch, while a voltage measurement is carried out on the winding (U) associated with the defective switch.