Torque Correction Circuit for PMSM Control
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Solution Overview
Problem
Permanent magnet synchronous motors, especially IPM motors, face challenges in maintaining accurate torque control across various speed operations due to complex calculations required for current command generation, leading to reduced control accuracy and increased CPU burden.
Innovation Solution
A control apparatus with a torque correction circuit that generates a torque correction command using the current phases of the d-axis and q-axis current commands, reducing the CPU burden by simplifying calculations and improving current command generation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex calculations are performed for current command generation in IPM motors, then torque control accuracy is improved, but CPU burden increases
Solution Approach 1:
The patent segments the torque control calculation into two parts: a d/q-axis current command generator that performs basic calculations using Formula (3), and a torque correction circuit that adds a correction term based on current phases. This segmentation allows the CPU to handle only the essential calculations while the correction circuit refines accuracy, reducing overall CPU burden while maintaining torque control precision.
Solution Approach 2:
The torque correction circuit acts as an intermediary between the basic current command generation and the final torque control. It introduces a correction term that accounts for the non-ideal characteristics of IPM motors without requiring the CPU to perform complex real-time calculations, thus bridging the gap between simplified control and accurate torque generation.
2Speed
If field weakening control is performed for high-speed operation, then voltage saturation is suppressed, but torque control accuracy deteriorates
Solution Approach 1:
The torque correction circuit uses feedback from the actual current phases (id and iq) to generate a correction term that compensates for torque control inaccuracies. During field weakening control at high speeds, this feedback mechanism adjusts the torque command based on the actual current state, counteracting the deterioration caused by d-axis current injection and maintaining accurate torque control across the speed range.
3Power
If d-axis current is increased in negative direction for field weakening control, then inverter output voltage saturation is suppressed, but torque generation efficiency decreases
Solution Approach 1:
The patent dynamically adjusts the torque command parameter by adding a correction term that depends on the current phases. This parameter change compensates for the efficiency loss caused by field weakening control, allowing the system to maintain optimal torque generation efficiency even when d-axis current is increased in the negative direction for high-speed operation.
Data Source
AI summary
A control apparatus for a permanent magnet synchronous motor capable of performing highly accurate torque control not only during low-speed operation and medium-speed operation but also during high-speed operation without increasing a burden on a product CPU irrespective of whether the permanent magnet synchronous motor is an SPM motor or an IPM motor. The control apparatus includes a torque correction circuit that generate a torque correction command from a current phase of current correction commands on a d-axis and a q-axis and a torque command and supplies the torque correction command to a d/q-axis current command generator instead of the torque command.