Vector Control Device Flux Command Switching for Harmonic Loss Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional vector control devices for electric motors experience increased harmonic loss due to ripple in synchronous PWM mode, limiting the operation region of asynchronous PWM mode and preventing reduction of harmonic loss.
Innovation Solution
A vector control device that adjusts flux commands based on modulation factor and output frequency, switching from asynchronous PWM mode to synchronous PWM mode only when the output frequency exceeds a predetermined value, allowing for flux weakening control in asynchronous mode to reduce harmonic loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If switching to synchronous PWM mode when modulation factor exceeds upper limit, then output voltage can be maintained, but harmonic loss due to ripple increases
Solution Approach 1:
The invention changes the switching criterion from modulation factor-based to output frequency-based. By using output frequency as the switching parameter, the system can maintain asynchronous PWM mode at higher modulation factors, thereby reducing harmonic loss while still achieving sufficient output voltage through frequency-dependent control strategies
2Loss of energy
If increasing operation region of asynchronous PWM mode by decreasing synchronous PWM mode region, then harmonic loss due to ripple can be reduced, but output voltage control becomes limited
Solution Approach 1:
The invention changes the control parameter from modulation factor to output frequency for determining PWM mode switching. This parameter change allows the system to expand asynchronous PWM operation region without compromising output voltage control, because the switching decision is now based on frequency characteristics rather than modulation factor limits
3Power
If using constant flux command control in asynchronous PWM mode, then output voltage can be increased, but modulation factor reaches upper limit quickly, limiting operation region
Solution Approach 1:
The invention introduces dynamic switching criteria based on output frequency rather than static modulation factor thresholds. This dynamic approach allows the system to adaptively determine when to switch between asynchronous and synchronous PWM modes, expanding the overall operation region while maintaining voltage control capability across different frequency ranges
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A vector control device that controls an electric power converter 2 that converts DC power to AC power and supplies the AC power to an AC electric motor 1, includes a vector control unit 3 computing an output voltage output from the electric power converter 2 according to vector control based on torque command and flux command and generating a PWM signal for controlling the electric power converter based on the output voltage, a first flux-command generation unit 11a generating a flux command for asynchronous PWM mode, and a second flux-command generation unit 11b generating a flux command for synchronous PWM mode. When an output frequency of the electric power converter 2 is lower than predetermined value, a flux command generated by the first flux-command generation unit 11a is input to the vector control unit 3, and when the output frequency of the electric power converter 2 is equal to or higher than predetermined value, a flux command generated by the second flux-command generation unit 11b is input to the vector control unit 3.