Motor Control Device Using PWM Signal Pattern for Magnetic Pole Position Estimation
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Solution Overview
Problem
Conventional methods for estimating the magnetic pole position of electric motors are inaccurate at low speeds and not versatile enough for various motor types, as they rely on specific signal generators and are influenced by motor parameters, making them difficult to apply universally.
Innovation Solution
A motor control device with an inverter circuit and a current detecting element that generates signals for phase current detection, using a PWM signal pattern to detect phase currents twice within a carrier wave period, allowing for precise estimation of magnetic pole position without external sensing signals, and adaptable to different motor types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional induced voltage computation is used for magnetic pole position estimation, then the system is simple and widely applicable, but estimation accuracy deteriorates in very low speed range
Solution Approach 1:
The patent combines two estimation approaches: the conventional induced voltage computation method and the high-frequency current-based method. The system switches between or synthesizes results from both methods to achieve accurate estimation across the entire speed range, particularly improving low-speed accuracy while maintaining the simplicity and versatility of the conventional approach.
2Measurement precision
If a sensing AC signal is applied to estimate rotor position, then low speed estimation accuracy is improved, but device complexity increases due to requiring a particular signal generator
Solution Approach 1:
The patent utilizes the existing high-frequency current components that are already present in the inverter output during normal PWM operation. Instead of adding a separate sensing signal generator, the system extracts position information from the self-generated high-frequency current ripple, thereby improving accuracy without increasing device complexity.
3Speed
If high frequency current components are used for magnetic pole position estimation, then responsiveness is improved and no external sensing signal is needed, but the magnitude of high frequency current depends on motor parameters reducing versatility
Solution Approach 1:
The patent implements a feedback mechanism where the system monitors the magnitude and characteristics of the high-frequency current components and adjusts the estimation algorithm accordingly. This feedback allows the system to adapt to different motor parameters while maintaining accurate position estimation across various motor types.
4Device complexity
If carrier frequency components are used for position estimation, then no sensing signal is required and control is simplified, but the high frequency current becomes a disturbance against fundamental voltage
Solution Approach 1:
The patent converts the harmful high-frequency current disturbance into a useful signal source for position estimation. By extracting position information from the existing high-frequency current ripple that would otherwise be considered noise or disturbance, the system achieves accurate estimation without requiring separate sensing signals or adding complexity to the control system.
Data Source
AI summary
A motor control device includes an inverter circuit having switching elements on/off controlled according to a predetermined PWM signal pattern to convert an input direct current to three-phase alternating current supplied to drive an electric motor. A phase current of the motor is detected based on a detection of the input direct current and the PWM signal pattern. A PWM signal generation unit which generates a three-phase PWM signal pattern to enable detecting two-phase currents twice in synchronization with four time-points within a carrier wave period of the PWM signal respectively and so that a detection of current follows a magnetic pole position of the motor. A current differential unit supplies, as current differential values, differences between twice detected current values regarding the two phases respectively, and a magnetic pole position estimation unit estimates the magnetic pole position of the motor based on the current differential values.