Motor PWM Phase Timing for Full Current Detection
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Solution Overview
Problem
Conventional motor control devices using two-phase modulation in inverter circuits face challenges in detecting all three-phase currents effectively, especially in regions with increased modulation factors, leading to incomplete current detection and reduced control accuracy.
Innovation Solution
A motor control device with a current detection timing point adjusting unit that adjusts detection timing based on the output voltage magnitude, allowing for variable timing in current detection, and a PWM signal generation unit that modifies duty cycles in both phase lag and lead directions for each phase, ensuring accurate detection of phase currents even in overmodulated states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If two-phase modulation is used to reduce switching loss, then switching loss is reduced, but current detection accuracy deteriorates in high modulation factor regions
Solution Approach 1:
The patent applies dynamics by making the current detection timing variable rather than fixed. The detection timing is dynamically adjusted based on the PWM signal phase and modulation factor, allowing the system to adapt to different operating conditions. This enables accurate current detection in high modulation factor regions while maintaining the benefits of two-phase modulation for reducing switching losses.
Solution Approach 2:
The patent changes the detection timing parameter dynamically based on the modulation factor and PWM phase. By adjusting this parameter according to operating conditions, the system maintains accurate current detection across different modulation levels without switching to three-phase modulation, thus preserving the low switching loss advantage.
2Device complexity
If conventional fixed timing current detection is used in two-phase modulation, then device complexity is reduced, but current detection completeness deteriorates in high output voltage regions
Solution Approach 1:
The patent implements dynamic adjustment of current detection timing based on the PWM signal phase and modulation factor. This dynamic approach ensures that all three phase currents can be detected even in high output voltage regions where fixed timing would fail, improving detection completeness without adding significant system complexity.
Solution Approach 2:
The system uses feedback from the PWM signal generation unit about the current phase and modulation factor to adjust the detection timing. This feedback mechanism ensures that the detection timing is continuously optimized to capture all phase currents accurately, maintaining reliability across different operating conditions.
Data Source
AI summary
A motor control device includes a PWM signal generation unit generating a signal pattern of two of three phases so that the pattern follows a rotor position, and a timing adjusting unit. The signal generation unit increases/decreases duty in both directions of lag side and lead side based on any phase of a carrier-wave period regarding a first phase. The signal generation unit increases/decreases duty in one direction regarding a second phase. The signal generation unit increases/decreases duty in a direction opposite to the second phase regarding a third phase. The timing adjusting unit adjusts detection timing so that a current detection unit detects current in fixed timing with respect to one phase and current in another fixed timing with respect to the other phase or the current detection unit is capable of detecting current in variable timing according to magnitude of output voltage to an inverter circuit.