Adaptive Current Detection Sequence for PWM Motor Control
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Solution Overview
Problem
In three-phase brushless motor control systems using pulse width modulation (PWM), accurate current detection can fail due to the short ON period of switching elements, leading to incorrect current measurements, especially when the A/D converter changes channels quickly and the PWM driving pattern restricts current detection within the ON period.
Innovation Solution
A control device that includes a driving unit for PWM operation, a detection unit for time-division current detection, and a change unit that adjusts the current detection sequence based on PWM duty cycles to ensure accurate detection, even at high rotation speeds and short sampling cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single A/D converter detects currents in fixed sequence (U, V, W phases) with time-division multiplexing, then device complexity is reduced and cost is lowered, but current detection accuracy deteriorates when PWM ON period is short
Solution Approach 1:
The patent applies dynamics by making the current detection sequence adaptive rather than fixed. The detection unit dynamically changes the detection order of U, V, W phases based on real-time PWM duty cycle information. When a phase has a short ON period, its detection is prioritized to occur within the available time window, ensuring accurate measurement while maintaining the cost-effective single A/D converter architecture.
Solution Approach 2:
The patent changes the parameter of detection sequence based on PWM duty cycle conditions. By monitoring the duty cycle of each phase, the system adjusts the detection order parameter dynamically - phases with shorter ON periods are detected earlier in the sequence, while phases with longer ON periods are detected later. This parameter adaptation resolves the contradiction between using a simple single converter and achieving accurate measurements under varying PWM conditions.
2Reliability
If PWM driving pattern is restricted to ensure current detection completes during ON period, then current detection reliability is improved, but driving flexibility and rotation speed capability are reduced
Solution Approach 1:
The patent eliminates the need for restrictive PWM patterns by implementing a dynamic detection sequence that adapts to any PWM duty cycle. The detection unit reorders phase detections based on real-time duty cycle information, allowing accurate current measurement regardless of how short or long the ON periods are. This dynamic adaptation maintains detection reliability while preserving full PWM driving flexibility and enabling higher rotation speeds.
Solution Approach 2:
The patent performs preliminary action by obtaining PWM duty cycle information in advance before current detection begins. Using this advance knowledge, the detection unit pre-calculates and sets the optimal detection sequence that ensures all phase currents are measured within their respective ON periods. This preliminary planning allows the system to handle any PWM pattern without restriction while maintaining reliable detection.
3Productivity
If A/D converter channel switching is performed quickly to maintain high rotation speed, then productivity is improved, but current detection accuracy deteriorates due to insufficient sampling time
Solution Approach 1:
The patent resolves this contradiction by dynamically adjusting the detection sequence based on PWM duty cycle. When rotation speed increases and PWM periods shorten, the system automatically prioritizes detection of phases with shorter ON periods. This dynamic reordering ensures that each phase current is sampled within its available time window, maintaining measurement accuracy even at high rotation speeds where the A/D converter must switch channels rapidly.
Solution Approach 2:
The patent changes the detection timing parameters adaptively based on operating conditions. By monitoring PWM duty cycle and rotation speed, the system adjusts which phases are detected first, second, or third in the sequence. This parameter change allows the A/D converter to allocate its limited sampling time efficiently across all three phases, maintaining both high-speed operation and accurate current measurement.
Data Source
AI summary
A control device comprises a driving unit configured to drive a plurality of coils of a multiple-phase motor by pulse width modulation; a detection unit configured to detect currents flowing through the plurality of coils in a time-division manner; and a change unit configured to change, in accordance with a duty in the pulse width modulation, a sequence of detecting the currents flowing through the plurality of coils by the detection unit.