Sensorless Rotor Position Estimation via Terminal Voltage Measurement
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Solution Overview
Problem
Existing position sensor-less control technologies for permanent magnet synchronous motors face challenges in accurately determining the rotor position, especially at low speeds and during abrupt load torque changes, due to elongated observation cycles and errors caused by induced voltages.
Innovation Solution
The system measures terminal voltage by turning off all switching devices of a three-phase inverter, allowing the motor current to flow through a free wheel diode, estimating the current decrease time to zero, and using this information to determine the rotor position without speed information, thereby reducing observation cycles and improving load follow-up performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If terminal voltage detection is performed by switching to 120-degree power feed driving, then rotor position can be estimated, but the observation cycle becomes elongated at low speeds
Solution Approach 1:
The patent applies dynamics by making the observation cycle adaptive to motor speed. At low speeds where the fixed 120-degree power feed observation cycle becomes too long, the system dynamically switches to a different power feed pattern that maintains appropriate observation frequency. This resolves the contradiction by adjusting the observation methodology based on operating conditions rather than using a fixed approach.
Solution Approach 2:
The patent changes the power feed pattern parameter from 120-degree to a different pattern when specific conditions are met (low speed operation). This parameter change allows the system to maintain adequate observation frequency for rotor position estimation even at low speeds, preventing the observation cycle from becoming excessively long while still enabling accurate position detection.
2Reliability
If terminal voltage is measured during normal 180-degree power feed driving, then continuous control is maintained, but speed electromotive force cannot be detected due to fixed inverter output potential
Solution Approach 1:
The patent implements periodic action by temporarily switching from 180-degree to 120-degree power feed driving at specific intervals to perform rotor position estimation. This periodic switching allows the system to maintain continuous control overall while creating dedicated measurement windows where speed electromotive force can be detected, thus resolving the contradiction between control continuity and measurement capability.
Solution Approach 2:
The patent uses the 120-degree power feed driving mode as an intermediary state that enables measurement functionality without permanently disrupting the normal 180-degree driving mode. This intermediary approach allows speed electromotive force detection to occur periodically while maintaining the benefits of continuous 180-degree control for the majority of operation time.
3Ease of operation
If terminal voltage is compared with reference potential to determine commutation timing, then simple control is achieved, but the method is limited to specific driving conditions
Solution Approach 1:
The patent applies dynamics by making the control method adaptive to different driving conditions. Instead of using a single fixed method (comparing terminal voltage with reference potential), the system dynamically selects between different approaches based on operating conditions such as motor speed and load state, thereby maintaining simplicity while expanding adaptability.
Solution Approach 2:
The patent changes the control parameter from a fixed reference potential comparison method to a conditional method that selects between different detection approaches. By changing the control strategy parameter based on operating conditions, the system maintains ease of operation through simple logic while achieving versatility across diverse driving scenarios.
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
This approach allows for precise rotor position estimation and improved load follow-up performance, even at low speeds, by eliminating induced voltage errors and maintaining consistent rotor position detection cycles during load changes.
Implementation Method 1
turning off all switching devices of a three-phase inverter, allowing the motor current to flow through a free wheel diode
Implementation Method 2
A voltage resulting from speed electromotive force of the motor appears in the terminal voltage of the phase that is under the power non-feed state
Data Source
AI summary
A driving apparatus of a synchronous motor fixes all the switching devices of an inverter at OFF in accordance with a value of an all-OFF control pulse signal outputted by a pulse generator. A motor current keeps flowing through free wheel diodes for a predetermined period even after all the switching devices shift to the OFF state. Therefore, pulse generator changes an induced voltage detection signal to an H (high) level after the passage of the time in which a motor current drops down to zero. A terminal voltage of the motor is taken in to acquire an induced voltage and a rotor position is estimated.