Motor Drive Device Zero-Axis Current Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing motor drive devices for open winding type motors face challenges in controlling zero-axis current, particularly when the three-phase unbalanced component of the induced voltage is non-zero, leading to significant zero-axis current flow that worsens losses and requires adjustment to ensure smoother torque, especially in permanent magnet type synchronous motors.
Innovation Solution
The motor drive device employs a control method that adjusts the zero-axis current by using a combination of Zero Common Mode Modulation (ZCMM) and non-ZCMM space vectors to manage the zero-axis current offset, allowing for intentional adjustment of the zero-axis current to desired values, even when the three-phase unbalanced component is present, thereby improving torque smoothness and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Zero Common Mode Modulation (ZCMM) is used to restrict space vectors to seven patterns with zero 0-axis voltage, then common mode voltage is eliminated, but the 0-axis current cannot be controlled when three-phase unbalanced component Ez is non-zero
Solution Approach 1:
The patent segments the control strategy into two distinct parts: ZCMM for eliminating common mode voltage and a separate 0-axis current control mechanism for managing zero-sequence current. This segmentation allows each control objective to be addressed independently without interfering with the other, resolving the contradiction between common mode elimination and 0-axis current controllability
Solution Approach 2:
The patent introduces an intermediary control mechanism that acts as a bridge between the ZCMM framework and 0-axis current control requirements. By adding a dedicated 0-axis voltage component through modified space vector selection, the system can control zero-sequence current while maintaining common mode voltage elimination in the αβ-plane
2Loss of energy
If significant 0-axis current flows when Ez is non-zero, then torque smoothness deteriorates and losses increase, but restricting to ZCMM space vectors prevents intentional adjustment of 0-axis current
Solution Approach 1:
The patent implements dynamic 0-axis current control by enabling real-time adjustment of the 0-axis voltage component through flexible space vector selection. The controller dynamically chooses from all 27 space vectors based on current operating conditions, allowing the 0-axis current to be intentionally adjusted to desired values for optimal torque smoothness and loss reduction
Solution Approach 2:
The patent changes the control parameter from fixed ZCMM restriction to variable space vector selection that includes 0-axis voltage components. By modifying the space vector selection criteria to consider 0-axis current requirements, the system can adjust 0-axis current magnitude and direction to minimize losses while maintaining effective torque control
3Adaptability or versatility
If all 27 space vectors are used for voltage control, then voltage flexibility is maximized, but 0-axis current becomes difficult to control
Solution Approach 1:
The patent applies partial action by selectively using only those space vectors that contribute to effective torque production while excluding or limiting the use of vectors that generate excessive 0-axis current. This selective approach maintains sufficient voltage flexibility for torque control while reducing 0-axis current issues, achieving optimal performance without requiring all 27 space vectors
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Provided is a motor drive device capable of adjusting a 0-axis current to a desired value. A motor drive device (inverter device 100) for an open winding type motor 200 in which a stator winding wire includes three-phase independent winding wires 210, 220, and 230 includes a plurality of single-phase inverters 160, 170, and 180 provided for each of the winding wires 210 to 230 to individually apply a voltage to a corresponding winding wire, and a controller 150 that controls each of the single-phase inverters 160 to 180. The controller 150 adjusts a 0-axis current to a predetermined value by alternately and repeatedly generating a first period in which a sum of voltages applied to the respective independent winding wires 210 to 230 is set to a value other than zero to offset the 0-axis current and a second period in which the sum of the voltages applied to the respective winding wires 210 to 230 is set to zero.