Motor Inverter Control Near Zero Current Dead-Time Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Control devices for electric motors face decreased controllability and increased losses due to high-frequency currents, particularly when alternating currents approach zero, leading to frequent polarity switches and reduced correction accuracy of voltage command values during dead time.
Innovation Solution
A control device that adjusts the d-axis current command value to be greater only during specific times before and after the alternating current reaches zero, and increases the carrier wave frequency during these times, thereby reducing the amplitude of high-frequency currents and minimizing polarity switches, thus enhancing correction accuracy and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the d-axis current command value is caused to be relatively great to increase alternating current amplitude and suppress polarity switching, then the correction accuracy of voltage command values during dead time is improved, but the current flowing through switching elements increases and loss increases
Solution Approach 1:
The patent applies dynamics by making the d-axis current command value variable rather than constant. Specifically, the control device increases the d-axis current command value only during specific periods when the alternating current approaches zero, rather than maintaining a high value continuously. This dynamic adjustment allows the system to suppress polarity switching only when necessary (near zero current points) while reducing current magnitude during other periods, thereby improving correction accuracy when needed while minimizing energy loss overall.
2Reliability
If the d-axis current command value is caused to be relatively great to increase the inclination of alternating currents near zero, then the frequency of polarity switching due to high-frequency current is suppressed, but the amplitude values of alternating currents increase and more current flows through switching elements
Solution Approach 1:
The patent applies periodic action by implementing periodic control of the d-axis current command value. The control device identifies specific periods within each AC cycle when the current approaches zero and increases the d-axis current command value only during these intervals. This periodic adjustment ensures that the inclination of alternating currents is increased only when needed to prevent polarity switching, while allowing current amplitude to be reduced during other periods, thus maintaining controllability while reducing overall current quantity through switching elements.
Data Source
AI summary
A control device for an electric motor includes an inverter circuit; and a control circuit that finds a voltage command value such that the d-axis current and the q-axis current approach a d-axis current command value and a q-axis current command value, and turns the plurality of switching elements on and off by using a drive signal in accordance with a result of comparison between the voltage command value and a carrier wave. The control circuit corrects the voltage command value by using a polarity of the alternating current during dead time, and causes the d-axis current command value in a certain length of time before and after the alternating current reaches zero to be greater than the d-axis current command value in a length of time other than the certain length of time.