PWM Signal Generating Unit for Three-Phase Current Detection
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Solution Overview
Problem
Existing motor control devices experience torque fluctuations and increased noise levels due to stepwise variations in motor current when shifting phase PWM signals for current detection, making it difficult to simultaneously detect all three phase currents effectively.
Innovation Solution
A motor control device with a PWM signal generating unit that adjusts duty phases within a carrier period to allow for synchronized detection of two-phase currents without phase substitution, using different waveforms for each phase and setting reference phases based on carrier amplitude, ensuring stable current detection even at varying motor voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase PWM signals are sequentially shifted for current detection, then all three phase currents can be detected within one carrier period, but stepwise variations occur in motor current causing torque fluctuations and increased noise
Solution Approach 1:
The patent applies periodic action by using a triangular wave carrier that alternates between increasing and decreasing phases. Current detection is performed periodically at specific timing points during each carrier period, switching between detecting currents in different phase combinations (e.g., U and V phases during increasing phase, V and W phases during decreasing phase). This periodic detection approach enables all three phase currents to be accurately measured without causing stepwise variations, as the detection is synchronized with the natural periodic waveform transitions rather than abruptly shifting PWM phases.
2Device complexity
If a single shunt resistance is used in the direct current part, then device complexity is reduced, but it becomes difficult to detect all three phase currents simultaneously without sequential shifting
Solution Approach 1:
The patent applies universality by making the single shunt resistance serve multiple detection functions. During the increasing phase of the triangular carrier, the shunt resistance detects currents in the U and V phases; during the decreasing phase, it detects currents in the V and W phases. By strategically selecting detection timing points during different phases of the same carrier cycle, one detection element accomplishes what would traditionally require three separate detection elements, thereby maintaining device simplicity while achieving complete three-phase current measurement capability.
Solution Approach 2:
The patent uses periodic action to enable the single shunt resistance to detect all three phase currents by performing detections at different timing points during each carrier period. The detection process alternates between detecting U and V phase currents during the increasing phase and V and W phase currents during the decreasing phase. This periodic switching of detection targets allows one detection element to gather information about all three phases over time, eliminating the need for multiple simultaneous detection elements.
3Measurement precision
If phase PWM signals are shifted to enable current detection, then current detection coverage is improved, but motor current stability deteriorates due to stepwise variations
Solution Approach 1:
The patent resolves the stability issue by eliminating abrupt PWM phase shifts and instead using periodic detection synchronized with the triangular carrier waveform. Current detection occurs periodically at specific points during the increasing and decreasing phases of the carrier, allowing the PWM signals to maintain their normal phase relationships without abrupt transitions. This approach preserves motor current stability while still achieving complete three-phase current detection coverage through the periodic sampling strategy.
Data Source
AI summary
A motor control device includes a PWM signal generating unit comparing PWM command voltage and carrier wave with each other to generate pulse signal so that duty is increased or decreased in both directions of phase lag and phase lead with one phase within carrier period as reference regarding one phase of three-phase PWM signal. The unit generates pulse signal so that duty is increased or decreased in one of the directions with one phase as reference regarding another phase. The unit generates pulse signal so that duty is increased or decreased in direction reverse to the one direction with one phase as reference regarding the other phase. The unit generates three-phase PWM signal pattern so that a current detecting unit is capable of detecting two-phase current in synchronization with advent of two predetermined time-points within carrier wave period of PWM signal with first to third phases being normally fixed.