Three-Phase PWM Control for Two-Phase Current Detection Timing
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Solution Overview
Problem
Conventional motor control devices using a three-phase bridge configuration inverter circuit can only detect one phase current effectively at two current detection timings when the modulation factor is increased, leading to reduced current detection accuracy and waveform distortion.
Innovation Solution
A motor control device with a current detecting element and a PWM signal generation unit that adjusts the duty cycle of the PWM signal in both phase lag and lead directions for each phase, allowing for two-phase current detection at variable timing points within the carrier period, even when the output voltage is high, thereby improving detection accuracy and reducing waveform distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the modulation factor is increased to improve output voltage, then the output voltage is improved, but only one phase current can be detected at two current detection timings
Solution Approach 1:
The patent dynamically adjusts the detection timing points based on the modulation factor. When the modulation factor exceeds a threshold, the system switches from fixed timing detection to variable timing detection, where the timing points are calculated to ensure two-phase current detection is possible. This dynamic adaptation resolves the contradiction by maintaining detection accuracy across varying output voltage levels.
Solution Approach 2:
The patent changes the detection timing parameters adaptively. Instead of using fixed timing points, the system calculates variable timing points based on the actual modulation factor and PWM signal patterns. This parameter change enables the system to detect two-phase currents even when the modulation factor is high, thereby maintaining measurement precision while allowing high output voltage operation.
2Device complexity
If conventional current detection timing is used, then the device complexity is low, but waveform distortion occurs when modulation factor is increased
Solution Approach 1:
The system performs self-adjustment of detection timing points based on its own operating conditions (modulation factor). The control unit automatically calculates and adjusts the timing points without external intervention, enabling the system to maintain waveform accuracy while operating at high modulation factors, all within the existing inverter circuit structure.
3Ease of operation
If fixed detection timing points are used, then the ease of operation is high, but current detection rate decreases at high output voltages
Solution Approach 1:
The system transitions from static fixed timing points to dynamic variable timing points that adapt to the modulation factor. This dynamic approach maintains ease of operation through automated control while significantly improving the current detection rate at high output voltages by ensuring detection timing points are always positioned where two-phase currents can be detected.
Data Source
AI summary
A motor control device includes a PWM signal generation unit configured to increase/decrease a duty in both directions of phase lag side and phase lead side regarding a first phase of three-phase PWM signal pattern. The PWM signal generation unit is configured to increase/decrease a duty in one of the directions of phase lag side and phase lead side regarding a second phase. The PWM signal generation unit is configured to increase/decrease a duty in a direction opposite to that of the second phase with reference to any phase of the carrier-wave period regarding a third phase. A timing point adjusting unit is configured to detect two-phase currents at timing points fixed in the carrier-wave period and to adjust a detection timing point so that the current is detectable at a variable timing point regarding at least one phase when the two-phase currents become undetectable at the fixed timing points.