Overcurrent Protection Circuit for Electric Motor Drive
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Solution Overview
Problem
The existing electric motor drive devices require multiple input ports for the CPU to manage different wire connection states of the stator winding, leading to reduced accuracy in overcurrent protection due to variations in digital transistor resistance, which restricts the motor's operational capacity.
Innovation Solution
An electric motor drive device with a wire connection switching unit, inverter, control device, and overcurrent protection circuit that includes multiple determination circuits for each wire connection state, a combining circuit, and an invalidation circuit to output a determination result for the selected state, preventing excessive current flow and enhancing protection accuracy without increasing CPU input ports.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If multiple input ports are provided for the CPU to manage different wire connection states, then the control capability is improved, but the device complexity and cost increase
Solution Approach 1:
The single input port is designed to handle multiple wire connection states (star and delta) through configuration data, making it universal for different connection types without requiring separate ports for each state
Solution Approach 2:
The system changes the threshold parameter based on the detected wire connection state, allowing the same input port to accurately monitor different states by dynamically adjusting the comparison threshold according to the connection type
2Adaptability or versatility
If digital transistors are used to switch determination circuits, then the switching capability is improved, but the measurement precision deteriorates due to resistance variations
Solution Approach 1:
Configuration data acts as an intermediary that conveys the wire connection state information to the CPU, enabling accurate threshold selection without the CPU directly reading analog signals that would be affected by transistor resistance variations
Solution Approach 2:
The system replaces direct analog signal reading with a digital configuration data-based approach, substituting the mechanical/electrical sensing method with a software-based threshold adjustment mechanism that is insensitive to transistor resistance variations
3Reliability
If the threshold value is set with large margin to account for transistor variations, then the reliability is improved, but the productivity deteriorates due to restricted motor operation
Solution Approach 1:
The threshold parameter is dynamically changed based on the wire connection state, allowing the system to operate at higher currents in delta connection without risking demagnetization, thus improving productivity while maintaining reliability through state-appropriate threshold selection
Data Source
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AI summary
An electric motor drive device includes: a wire connection switching unit switching the wire connection state of the stator winding; an inverter; a control device controlling the wire connection switching unit and the inverter; and an overcurrent protection circuit (60) preventing current exceeding a predetermined value from continuously flowing through the electric motor. The overcurrent protection circuit includes: a first determination circuit (62) and a second determination circuit (63) that are determination circuits each correlated one-to-one with any one of possible wire connection states of the stator winding and determining whether current flowing through the inverter is abnormal; a combining circuit (66) combining determination results in the determination circuits; and an invalidation circuit (65) invalidating a determination process by one or more of the determination circuits, and causing the combining circuit to output a determination result by the determination circuit correlated with a selected wire connection state of the stator winding. When the determination result output from the combining circuit indicates an abnormal value of the current flowing through the inverter, the control device stops the inverter.