Motor Controller PWM Timing for Low-Speed Sensorless Pole Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for estimating the magnetic pole position of electric motors without position sensors face challenges in low-speed regions due to reduced induced voltage amplitude and noise interference, and require specialized microcontrollers for generating complex PWM signals, limiting broad application.
Innovation Solution
An electric motor controller uses a triangular wave carrier for generating PWM signals, shifting duty ratios of phases to detect current changes at specific timings, enabling accurate magnetic pole position estimation without sensors, even at low speeds, using a common microcontroller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an induced voltage-based method is used to estimate magnetic pole position, then accuracy is sufficient in high-speed region, but the amplitude of induced voltage becomes smaller or not generated in low-speed region, hindering accurate estimation
Solution Approach 1:
The patent changes the estimation method parameter based on speed conditions. At low speeds where induced voltage is insufficient, it switches to an inductance-based estimation method using alternating-current voltage signals. At high speeds where induced voltage is sufficient, it uses the induced voltage-based method. This parameter change resolves the contradiction by adapting the estimation approach to the operating speed condition.
2Measurement precision
If an inductance-based method using alternating-current voltage signal is used to estimate magnetic pole position, then estimation is possible in low-speed region, but increased noise occurs since the frequency of current ripples is within the human audible range
Solution Approach 1:
The patent changes the frequency parameter of the alternating-current voltage signal used for inductance-based estimation. By selecting a frequency higher than the carrier frequency (e.g., several kHz to several tens of kHz), it moves the measurement frequency away from the human audible range (20-20kHz), thereby reducing noise while maintaining estimation accuracy in low-speed regions.
3Measurement precision
If duty ratio of phases is increased or decreased in both directions with carrier wave period as reference to generate harmonic current amplitudes, then magnetic pole position can be estimated while suppressing noise, but specialized microcontroller is required to generate complex PWM signals, limiting broad application
Solution Approach 1:
The patent designs a PWM signal generation method that can be implemented on common microcontrollers without specialized hardware. By using standard PWM generation capabilities and implementing the duty ratio adjustments through software control of conventional PWM modules, it achieves noise suppression and accurate estimation while maintaining broad applicability across different microcontroller platforms.
4Measurement precision
If three-phase PWM signals are generated with different carrier waveforms for respective phases, then current change amounts can be detected accurately, but phases must be output in specific manner requiring specialized microcontroller
Solution Approach 1:
The patent introduces asymmetric duty ratio adjustments among the three phases by shifting the duty ratios in different directions (increase/decrease) relative to the carrier wave period. This asymmetric control creates detectable current change amounts while using only a single triangular carrier waveform, eliminating the need for complex different carrier waveforms and specialized microcontrollers.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Accurate magnetic pole position estimation is achieved across various speeds, including zero speed, with reduced noise and simplified microcontroller requirements, facilitating broader system applicability.
Implementation Method 1
an inverter circuit that performs on/off control of a plurality of switching elements connected by a three-phase bridge in accordance with predetermined PWM signal patterns so as to drive an electric motor
Implementation Method 2
a current detector that generates a signal corresponding to a current value of the inverter circuit
Implementation Method 3
a magnetic pole position estimation unit that estimates a magnetic pole position of the electric motor based on current change amounts
Data Source
AI summary
An electric motor controller of an embodiment includes: a PWM signal generation unit that generates three-phase PWM signal patterns to follow a magnetic pole position of the motor; a current detection unit that detects a phase current of the motor; a current change amount detection unit that outputs a difference between current values detected twice for each of two phases, as current change amounts; and a magnetic pole position estimation unit that estimates a magnetic pole position of the motor based on the current change amounts. The PWM signal generation unit uses a triangular carrier wave, generates three-phase PWM signal patterns to allow the current detection unit to detect current of each two phase twice at timing of four points within a carrier wave period of the PWM signal, shifts a maximum phase in one direction of an advancing or delay side, and oppositely shifts a medium phase.