Motor Control Apparatus PWM Phase-Shift Noise Reduction
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Solution Overview
Problem
Conventional motor control apparatuses experience unintended duty variations and current distortions due to PWM phase-shifts, leading to noise, vibration, and compromised steering performance in electric power steering systems, particularly when using a 1-shunt type current detecting circuit.
Innovation Solution
A motor control apparatus that employs a 1-shunt type current detecting circuit to determine duty command values and adjust PWM signal timings, utilizing a comparing section to assess duty command value relations and a timing control section to sequence rising or falling edges, along with a motor angle estimation section that uses past values for linear approximation to minimize angle detection variations during phase-switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM phase-shift is applied to control motor current, then current control precision is improved, but duty variation and noise are generated
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal PWM phase-shift amounts in a lookup table before operation. The phase-shift amount determination section retrieves the appropriate phase-shift value based on current operating conditions (current command value and detection timing), eliminating the need for real-time calculation and preventing duty variation caused by dynamic phase-shift adjustments.
Solution Approach 2:
The patent introduces an intermediary element (the predetermined phase-shift amount from lookup table) between the PWM control signal and the motor current detection. This intermediary phase-shift value acts as a mediator that smooths the transition between different PWM phases, preventing abrupt duty variations while maintaining effective current control.
2Device complexity
If 1-shunt type current detecting circuit is used, then device complexity and cost are reduced, but measurement precision of motor current is compromised
Solution Approach 1:
The patent applies feedback by continuously monitoring the motor current detection timing and using this information to select appropriate PWM phase-shift amounts from the lookup table. The phase-shift amount determination section uses feedback from the current detection timing to adjust the phase-shift value, compensating for the limitations of the 1-shunt circuit and maintaining measurement precision.
Solution Approach 2:
The patent changes parameters by dynamically adjusting the PWM phase-shift amount based on operating conditions (current command value magnitude and detection timing). By varying the phase-shift parameter according to the specific operating state, the system optimizes current detection accuracy across different load conditions while using the simpler 1-shunt circuit configuration.
3Speed
If motor angle signal from rotation sensor is used at duty pattern switching timing, then control responsiveness is improved, but noise and angle variation influence are introduced
Solution Approach 1:
The patent extracts and removes the problematic motor angle signal from the rotation sensor at duty pattern switching timing. Instead of using the sensor signal during switching transitions, the system excludes this noisy data and relies on previously stored motor angle information, eliminating the source of noise and angle variation interference.
Solution Approach 2:
The patent applies preliminary action by storing motor angle information in advance before duty pattern switching occurs. The stored motor angle data is prepared beforehand and made available for use during switching transitions, ensuring continuous control without introducing noise from real-time sensor readings at critical switching moments.
Data Source
AI summary
A motor control apparatus that calculates duty command values of respective phases for controlling currents of a motor by means of a control calculation, forms PWM-signals in correspondence to the duty command values, drives the motor by means of an inverter based on the PWM-signals, and which is provided a rotation sensor to detect a motor angle of the motor.