Motor Controller PWM Signal Adjustment for Current Detection
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Solution Overview
Problem
Conventional motor control systems experience distortion in current waveforms due to phase changes in PWM signals, leading to unwanted noise and discomfort in applications connected to motors.
Innovation Solution
A motor controller that adjusts the duty cycles and generates PWM signals for three phases, ensuring that the energization periods align to allow detection of phase currents, thereby reducing current distortion and noise by maintaining a consistent time sequence order of PWM signal changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM signal phase changes are made to detect currents for multiple phases within one PWM period, then current detection capability is improved, but current waveform distortion occurs causing unwanted sound and noise
Solution Approach 1:
The patent applies preliminary action by pre-defining fixed phase shift amounts for PWM signals before current detection. The control unit determines detection timing based on these predetermined phase shifts, ensuring that PWM phase changes are planned in advance rather than occurring arbitrarily. This allows the system to detect currents for multiple phases within one PWM period while maintaining predictable current waveforms, thereby resolving the contradiction between improved current detection capability and reduced unwanted sound and noise.
2Measurement precision
If PWM signals are adjusted to enable detection of phase currents for all three phases, then measurement completeness is improved, but energization time periods become difficult to detect due to overlapping timing
Solution Approach 1:
The patent applies segmentation by dividing the PWM period into distinct energization time periods for each phase, with each phase having its dedicated detection window. The control unit determines specific detection timing for each phase based on predetermined phase shifts, creating separate non-overlapping detection intervals. This segmentation allows complete detection of all three phase currents while maintaining clear identification of each energization time period, resolving the contradiction between measurement completeness and detection difficulty.
3Reliability
If zero vector period is extracted and assigned to adjust energization width, then current detection reliability is improved, but PWM signal complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the energization width parameter of PWM signals through extraction and assignment of zero vector periods. The control unit adjusts the duration of energization time periods by incorporating zero vector period portions, which changes the temporal parameters of PWM signals. This parameter adjustment ensures reliable current detection by providing adequate energization width while maintaining a relatively simple PWM generation approach, resolving the contradiction between detection reliability and signal complexity.
Data Source
AI summary
A motor controller 100-1 includes an inverter, a current detection unit, a current detector, and a PWM signal generator. Upon occurrence of a condition in which a first energization time period, which has an energization width in which a phase current for a first phase is detectable by the current detector, and a second energization time period, which has an energization width in which a phase current for a second phase is difficult to be detected by the current detector, are present, the PWM signal generator extracts a portion of a zero vector period for a first PWM signal, a second PWM signal, and a third PWM signal, to assign an energization width corresponding to the extracted zero vector period, to a period, other than the zero vector period, for a given PWM signal among the first PWM signal, the second PWM signal, and the third PWM signal, so that the second energization time period is adjusted to have an energization width in which the phase current for the second phase is detectable by the current detector.