Sensorless Motor Drive Using Neutral Point Potential Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing sensor-less control methods for permanent magnet motors face challenges in accurately detecting rotor position at low speeds due to sensitivity issues and noise interference, particularly when using induced voltage detection, which requires expensive insulating amplifiers and is not suitable for consumer or industrial applications.
Innovation Solution
An electric motor drive device that detects the neutral point potential of a three-phase synchronous motor without an insulating amplifier by setting the ground potential to a DC voltage reference, using differential amplifiers and A/D converters to estimate rotor position based on differences between neutral point potentials and fixed reference potentials, allowing for accurate position estimation even at ultra-low speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If induced voltage detection is used for sensor-less control, then position information can be obtained during normal PWM operation, but sensitivity decreases and position information becomes buried in noise during low speed operation
Solution Approach 1:
The patent introduces an insulating amplifier as an intermediary device between the neutral point potential detection circuit and the control unit. This amplifier isolates the high-voltage motor control circuit from the low-voltage control unit, enabling accurate detection of small neutral point potential variations even during low-speed operation without direct electrical connection, thus resolving the sensitivity and noise issues.
Solution Approach 2:
The patent replaces traditional mechanical or direct electrical connection-based position sensing methods with an electrical field-based neutral point potential detection method. By detecting voltage variations in the neutral point through an insulating amplifier, the system achieves non-contact, sensor-less position detection that maintains accuracy across all speed ranges.
2Measurement precision
If neutral point potential detection with insulating amplifier is implemented, then accurate position information can be obtained at low speeds, but system cost increases due to expensive insulating amplifier requirement
Solution Approach 1:
The insulating amplifier serves as a necessary intermediary that enables accurate low-speed detection. While it increases component count, its integration into the existing PWM control architecture minimizes additional complexity, and the use of standard insulating amplifier designs helps control costs.
Solution Approach 2:
The insulating amplifier performs multiple functions: it provides electrical isolation between high and low voltage circuits, amplifies the small neutral point potential signals for accurate detection, and maintains signal integrity during low-speed operation. This multi-functionality justifies its inclusion despite the added cost.
3Device complexity
If ground potential is set to negative side or positive side of DC voltage, then insulating amplifier can be eliminated and system simplified, but neutral point potential detection becomes more complex
Solution Approach 1:
Instead of using a virtual neutral point as ground reference (which requires insulating amplifier), the patent inverts the approach by directly using either the positive or negative DC bus voltage as the ground reference. This eliminates the need for electrical isolation since the control unit ground is now referenced to the same potential as the motor drive circuit.
Solution Approach 2:
The patent changes the reference potential parameter from a virtual neutral point (0V) to an actual DC bus voltage (+Vdc or -Vdc). This parameter change fundamentally alters the detection methodology, allowing direct measurement of neutral point potential without insulation requirements, though requiring differential measurement techniques to handle the higher voltage range.
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
Enables high-accuracy neutral point potential detection and sensor-less driving with sine wave currents from zero speed regions without the need for insulating amplifiers, making it cost-effective and suitable for various applications, including consumer and industrial use.
Implementation Method 1
a neutral point potential detection unit that detects a neutral point potential of a stator winding of the three-phase synchronous electric motor
Implementation Method 2
a control unit that estimates a rotor position of the three-phase synchronous electric motor based on the detected neutral point potential
Data Source
AI summary
An electric motor drive device 1000 includes: an inverter 3 that drives a motor 4, a voltage division circuit 2 that serves as a neutral point potential detection unit that detects a neutral point potential of a stator winding of the motor 4; and a controller 1 that estimates a rotor position of the motor 4 based on the detected neutral point potential, and that controls the inverter 3 based on an estimation result. A ground potential of the controller 1 is set to a negative side potential or a positive side potential of a DC voltage that is supplied to the inverter 3. The voltage division circuit 2 detects the neutral point potential with reference to the negative side potential or the positive side potential. The controller 1 estimates the rotor position based on a difference between a first neutral point potential detected during the ON/OFF operation of the inverter 3 and a first fixed reference potential (⅔)Emax, and based on a difference between a second neutral point potential detected during the ON/OFF operation and a second fixed reference potential (⅓)Emax.