Motor driving apparatus
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Solution Overview
Problem
Existing motor driving apparatuses face challenges in providing appropriate over-current protection for permanent magnet synchronous motors, particularly when switching between star and delta connection states, due to manufacturing variations in transistors and the resulting accuracy and cost issues, as well as high processing loads on CPUs.
Innovation Solution
A motor driving apparatus with a single output over-current protection circuit that includes multiple decision circuits for different connection states, a combining circuit to integrate their outputs, and a nullifying circuit to adjust threshold values, allowing for high-speed protection with reduced hardware costs and CPU processing loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate comparison circuits and CPU processing are used for different connection states, then over-current protection accuracy is improved, but device complexity and processing load increase
Solution Approach 1:
The patent combines multiple comparison circuits into a single integrated circuit that can handle both star and delta connection states. The integrated circuit uses a single current detection line and performs both threshold comparisons internally, eliminating the need for separate comparison circuits and reducing CPU processing load while maintaining protection accuracy for both connection states.
2Measurement precision
If transistors with smaller variations are used to improve protection accuracy, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the approach from relying on transistor manufacturing precision to using circuit topology and threshold voltage design. By using a single current detection line and carefully designed threshold voltages that account for the √3 current ratio difference between connection states, the system achieves accurate protection without requiring expensive low-variance transistors.
3Reliability
If the threshold value is set lower to account for transistor variations, then reliability is improved, but power output capability decreases
Solution Approach 1:
The patent performs preliminary action by pre-calculating and setting appropriate threshold voltages for each connection state within the integrated circuit. The circuit is designed to recognize the connection state and automatically apply the correct threshold, allowing the system to operate at optimal power levels for each state while maintaining reliable protection, rather than using a conservatively low threshold for all states.
Data Source
AI summary
An over-current protection circuit for a motor capable of selecting one of a plurality of connection states has a plurality of decision circuits, a combining circuit, and a nullifying circuit. The combining circuit combines results of the comparisons in the plurality of decision circuits. The nullifying circuit nullifies part of the comparisons in the plurality of decision circuits. The number of outputs of the over-current protection circuit is one, so that for controlling the driving and stopping of the inverter needs just one terminal is required for receiving the output of the combining circuit. Moreover, because the over-current protection circuit is formed of hardware, the protection can be performed at a high speed.